Hmm... I wonder what is different between our setups. I can play and convert AAC-LC/m4a files just fine through Haali & FFDShow (CCCP 2007-07-22). The Haali & FFDshow audio decoder icons show up and I don't get any error messages. I have not configured MC's DS playback anyhow except enabling it for this format.
Here's a log of an m4a to mp3 conversion if you want to compare the logs.
Media Center; Version: 12.0.382; Types: 16383
0000000: 5860: General: Starting logging: Date: 12/4/2007 12:34:56 PM
0000000: 5860: General: Log Reset: Logging reset
0001640: 5860: General: CMCResourceHelper::GetIsModalPopupShowing: Main window disabled
0005468: 5860: General: CMCResourceHelper::GetIsModalPopupShowing: Menu showing
0005500: 5860: Reader: CLocalReader::OpenInternal: Opening: C:\Soft\MC12\Data\Default Art\Converter.png
0005515: 5860: Reader: CLocalReader::Close: Closing: C:\Soft\MC12\Data\Default Art\Converter.png
0006953: 5860: Reader: CLocalReader::OpenInternal: Opening: C:\Soft\MC12\Data\Default Art\OptionsTree.png
0006968: 5860: Reader: CLocalReader::Close: Closing: C:\Soft\MC12\Data\Default Art\OptionsTree.png
0007015: 5860: Playback: CWaveFeederHelper::GetForceDirectShow: Returning FALSE for file X:\Super Furry Animals\Songbook The Singles\09 - Play It Cool.m4a
0007015: 5860: Playback: CDShowFileRenderer::RenderFile: Start
0007015: 5860: Playback: CDShowFileRenderer::LoadSourceFilter: Start
0007015: 5860: Playback: CDShowFileRenderer::LoadSourceFilter: Finish (0 ms)
0007015: 5860: Playback: CDShowFileRenderer::RenderFile: LoadSourceFilter returned 0x80004005
0007015: 5860: Playback: CDShowFileRenderer::LoadTransformFilters: Start
0007015: 5860: Playback: CDShowFileRenderer::LoadTransformFilters: Finish (0 ms)
0007015: 5860: Playback: CDShowFileRenderer::RenderFile: LoadTransformFilters returned 0x1
0007015: 5860: Playback: CDShowFileRenderer::LoadSourceFilter(2): Start
0007015: 5860: Playback: CDShowFileRenderer::LoadSourceFilter(2): Finish (0 ms)
0007015: 5860: Playback: CDShowFileRenderer::LoadSourceFilter(2): Start
0007015: 5860: Playback: CDShowFileRenderer::LoadSourceFilter(2): Added the filter to graph
0007015: 5860: Playback: CDShowFileRenderer::LoadFileUsingSourceFilter: Start
0007047: 5860: Playback: CDShowFileRenderer::LoadFileUsingSourceFilter: Load returned 0x0
0007047: 5860: Playback: CDShowFileRenderer::LoadFileUsingSourceFilter: Finish (32 ms)
0007047: 5860: Playback: CDShowFileRenderer::LoadSourceFilter(2): Finish (32 ms)
0007312: 5860: Playback: CDShowFileRenderer::RenderFile: RenderOutputPins returned 0x0
0007312: 5860: Playback: CDShowFileRenderer::RenderFile: Finish (297 ms)
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: Audio out MediaType M type MEDIATYPE_Audio S type MEDIASUBTYPE_PCM
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: Subtype description UNKNOWN
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: Not temporally compressed
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: Sample size 1
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: Format type FORMAT_WaveFormatEx
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: Subtype MEDIASUBTYPE_PCM
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: wFormatTag 1
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: nChannels 2
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: nSamplesPerSec 44100
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: nAvgBytesPerSec 176400
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: nBlockAlign 4
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: wBitsPerSample 16
0007312: 5860: Playback: 0x16e4 DisplayTypeEx: cbSize 0
0007375: 3356: Playback: CWaveOutBinPlayThread::Thread: Start
0007390: 5860: Playback: 0x16e4 DumpGraph: Start
0007390: 5860: Playback: 0x16e4 DumpGraph: DumpGraph [39128]
0007390: 5860: Playback: 0x16e4 DumpGraph: Filter [1152844] 'MJ WaveBin Filter'
0007390: 5860: Playback: 0x16e4 DumpGraph: Pin [10c1a1c] 'In' [Input] Connected to pin [7fed0160]
0007390: 5860: Playback: 0x16e4 DumpGraph: Filter [7fed0050] 'DC-Graphic EQ Filter'
0007390: 5860: Playback: 0x16e4 DumpGraph: Pin [7fee00a0] 'Input' [Input] Connected to pin [3fe74]
0007390: 5860: Playback: 0x16e4 DumpGraph: Pin [7fed0160] 'Output' [Output] Connected to pin [10c1a1c]
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: Connection type M type MEDIATYPE_Audio S type MEDIASUBTYPE_PCM
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: Subtype description UNKNOWN
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: Not temporally compressed
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: Sample size 1
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: Format type FORMAT_WaveFormatEx
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: Subtype MEDIASUBTYPE_PCM
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: wFormatTag 1
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: nChannels 2
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: nSamplesPerSec 44100
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: nAvgBytesPerSec 176400
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: nBlockAlign 4
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: wBitsPerSample 16
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: cbSize 0
0007390: 5860: Playback: 0x16e4 DumpGraph: Filter [92b3014] 'AC3Filter'
0007390: 5860: Playback: 0x16e4 DumpGraph: Pin [3fd5c] 'In' [Input] Connected to pin [512b8dc]
0007390: 5860: Playback: 0x16e4 DumpGraph: Pin [3fe74] 'Out' [Output] Connected to pin [7fee00a0]
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: Connection type M type MEDIATYPE_Audio S type MEDIASUBTYPE_PCM
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: Subtype description UNKNOWN
0007390: 5860: Playback: 0x16e4 DisplayTypeEx: Not temporally compressed
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Sample size 1
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Format type FORMAT_WaveFormatEx
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Subtype MEDIASUBTYPE_PCM
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: wFormatTag 1
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nChannels 2
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nSamplesPerSec 44100
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nAvgBytesPerSec 176400
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nBlockAlign 4
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: wBitsPerSample 16
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: cbSize 0
0007406: 5860: Playback: 0x16e4 DumpGraph: Filter [9665694] 'ffdshow Audio Decoder'
0007406: 5860: Playback: 0x16e4 DumpGraph: Pin [512b8dc] 'Out' [Output] Connected to pin [3fd5c]
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Connection type M type MEDIATYPE_Audio S type MEDIASUBTYPE_PCM
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Subtype description UNKNOWN
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Not temporally compressed
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Sample size 1
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Format type FORMAT_WaveFormatEx
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Subtype MEDIASUBTYPE_PCM
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: wFormatTag 1
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nChannels 2
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nSamplesPerSec 44100
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nAvgBytesPerSec 176400
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nBlockAlign 4
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: wBitsPerSample 16
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: cbSize 0
0007406: 5860: Playback: 0x16e4 DumpGraph: Pin [512b53c] 'In' [Input] Connected to pin [4ec41c4]
0007406: 5860: Playback: 0x16e4 DumpGraph: Pin [512bd9c] 'In2' [Input]
0007406: 5860: Playback: 0x16e4 DumpGraph: Filter [4ec3e54] 'Haali Media Splitter'
0007406: 5860: Playback: 0x16e4 DumpGraph: Pin [4ec41c4] 'Audio' [Output] Connected to pin [512b53c]
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Connection type M type MEDIATYPE_Audio S type Unknown GUID Name
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Subtype description UNKNOWN
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Not temporally compressed
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Variable size samples
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Format type FORMAT_WaveFormatEx
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: Subtype Unknown GUID Name
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: wFormatTag 255
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nChannels 2
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nSamplesPerSec 44100
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nAvgBytesPerSec 176400
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: nBlockAlign 4
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: wBitsPerSample 16
0007406: 5860: Playback: 0x16e4 DisplayTypeEx: cbSize 2
0007406: 5860: Playback: 0x16e4 DumpGraph: Finish (16 ms)
0007437: 5860: Playback: CDXWaveFeeder::OnGraphNotify: Start: Thread: 0x16e4, Graph: 0x39128
0007437: 5860: Playback: CDXWaveFeeder::OnGraphNotify: Event 30 param1 0, Param2 0
0007437: 5860: Playback: CDXWaveFeeder::OnGraphNotify: Event 13 param1 0, Param2 0
0007437: 5860: Playback: CDXWaveFeeder::OnGraphNotify: End: Thread: 0x16e4, Graph: 0x39128, 0ms
0007437: 5860: Playback: CDXWaveFeeder::OnGraphNotify: Start: Thread: 0x16e4, Graph: 0x39128
0007437: 5860: Playback: CDXWaveFeeder::OnGraphNotify: End: Thread: 0x16e4, Graph: 0x39128, 0ms
0015406: 5860: Playback: CDXWaveFeeder::OnGraphNotify: Start: Thread: 0x16e4, Graph: 0x39128
0015406: 5860: Playback: CDXWaveFeeder::OnGraphNotify: Event 1 param1 0, Param2 0
0015406: 5860: Playback: CDXWaveFeeder::OnGraphNotify: EC_COMPLETE event
0015406: 5860: Playback: CDXWaveFeeder::OnGraphNotify: IMediaControl::Stop returned 0x0
0015484: 5860: Playback: CDXWaveFeeder::OnGraphNotify: End: Thread: 0x16e4, Graph: 0x0, 78ms
0015609: 5860: Playback: CWaveOutBinPlayThread::~CWaveOutBinPlayThread: Start
0015656: 3356: Playback: CWaveOutBinPlayThread::Thread: Finish (8281 ms)
0015672: 5860: Playback: CWaveOutBinPlayThread::~CWaveOutBinPlayThread: Finish (63 ms)
0015687: 5860: Import: JRAnalyzer::Open: Start
0015687: 5860: Import: JRAnalyzer::AddFile: Start
0015687: 5860: Import: JRAnalyzer::AddFile: Filename: E:\Rip\Super Furry Animals\Songbook_ The Singles Vol 1\09 - Play It Cool.mp3
0015687: 5860: Import: JRAnalyzer::AddFileMJ: Start
0015687: 5860: Import: JRAnalyzer::AddFileMJ: Finish (0 ms)
0015687: 5860: Import: JRAnalyzer::AddFile: Finish (0 ms)
0015687: 5860: Import: JRAnalyzer::Open: Finish (0 ms)
0015687: 5860: Reader: CLocalReader::OpenInternal: Opening: E:\Rip\Super Furry Animals\Songbook_ The Singles Vol 1\09 - Play It Cool.mp3
0015687: 5860: Reader: CLocalReader::Close: Closing: E:\Rip\Super Furry Animals\Songbook_ The Singles Vol 1\09 - Play It Cool.mp3
0015687: 5860: General: CFileImageHelper::SaveImageToExternalFile(0): Start
0015687: 5860: General: CFileImageHelper::SaveImageToExternalFile(0): Source file image: 'X:\Super Furry Animals\Songbook The Singles\Super Furry Animals - Songbook.jpg'
0015687: 5860: General: CFileImageHelper::SaveImageToExternalFile(0): Finish (0 ms)
0016890: 5860: General: CMJFileListCtrl::StartFileInsertion: Start
0016937: 5860: General: CMJFileListCtrl::StartFileInsertion: Finish (47 ms)
0016937: 5860: General: CMJFileListCtrl::FinishFileInsertion: Start
0016984: 5860: General: CMJFileListCtrl::FinishFileInsertion: Finish (47 ms)