5.1 Surround Sound Output Not Working From Late-2011 15" MacBook Pro

I just picked up a Sony HT-DW995 Reciever/Home Theater speaker system and I have been trying to play 5.1 audio from my computer. I also have a TV that i use as a secondary display via a thunderbolt/HDMI adapter. The HDMI cable runs through the reciever and then back out to the TV. Before I got the reciever, audio could pass through the HDMI cable and on to the TV with the visual just fine. All I get now is subwoofer and 2 speakers worth of audio coming out of my computer. I have tried rebooting, messing with the System Settings>Audio>Output settings, and messing with the Audio MIDI Setup settings, but nothign has worked. In the Audio MIDI setup is seems like it might work, but any audio options beyond stere are greyed out. I have also tried 5.1 output via DVD Player and VLC, but can't find the option for that in the Preferences window of those programs. I don't even need true 5.1, but I would like for sound to come out of all five speakers and the subwoofer, not just two and the subwoofer. Any ideas?

Late 2011 15 MBP

2.2 GHz i7, 4GB RAM, 10.8.3

All seems like it should be in order, but it's not.