Success!
I uninstalled AC3File and ffdshow and then installed the latest versions that I could find:
AC3File 0.7b
ffdshow_rev3078_20090917
Now .AC3 files play just fine in both MC13 and MC14.
A big thanks to Jim, Yaobing and especially Alex for the suggestions and information. I was getting pretty frustrated this morning and re-reading the posts helped.
Just in case it helps anyone else in similar situation in the future, here is the DS graph that I copied from MC14 while successfully playing the AC3 file:
Filter Graph Info (Graph for type: ac3):
Filter 'JRiver Audio Renderer'
CLSID: {EC1F74A8-7E55-4814-9F9F-D417489075CA}
Host:
Input Pin 'In'
Connected to pin 'Out' of filter 'ffdshow Audio Decoder'
Major type MEDIATYPE_Audio Sub type MEDIASUBTYPE_PCM, Format type FORMAT_WaveFormatEx
Filter 'ffdshow Audio Decoder'
CLSID: {0F40E1E5-4F79-4988-B1A9-CC98794E6B55}
Host: C:\Program Files (x86)\ffdshow\ffdshow.ax
Output Pin 'Out'
Connected to pin 'In' of filter 'JRiver Audio Renderer'
Major type MEDIATYPE_Audio Sub type MEDIASUBTYPE_PCM, Format type FORMAT_WaveFormatEx
Input Pin 'In'
Connected to pin 'Output' of filter 'AC3File'
Major type MEDIATYPE_Audio Sub type MEDIASUBTYPE_DOLBY_AC3, Format type FORMAT_WaveFormatEx
Filter 'AC3File'
CLSID: {F7380D4C-DE45-4F03-9209-15EBA8552463}
Host: C:\Program Files (x86)\AC3File\ac3file.ax
Output Pin 'Output'
Connected to pin 'In' of filter 'ffdshow Audio Decoder'
Major type MEDIATYPE_Audio Sub type MEDIASUBTYPE_DOLBY_AC3, Format type FORMAT_WaveFormatEx