It worked before? Are you sure MC wasn't upconverting or something? Are you testing with exactly the same sources?
I don't know the answer, just more questions, but...
It can be a bit of a challenge when the source can't be put into Exclusive mode, such as with YouTube and I suspect DirectTV, although I saw a comment that DirectTV was beta testing 5.1 Channel support. Windows DirectSound can get in the way, even if the WDM Driver is set to 5.1 Channels I suspect.
Try with a known 5.1 YouTube sample like
https://www.youtube.com/watch?v=eL9-sIZRDHg and see if you can get it to work. Note that as far as I know YouTube only supports Stereo, and so only encoded audio will produce multichannel audio, such as DTS in this sample or Dolby Digital. So the source (YouTube) is Stereo, MC receives Stereo, decodes that to 5.1 Channel, and will show 5.1 Channel in the Audio Path inside MC.
I'm not at my 5.1 channel system at the moment, but might have a look later using that sample above.
Also, you may want to Google "does youtube support 5.1". You will find some interesting reading.