Thunderbolt to HDMI 5.1 audio

[priest64]

I seem to be I seem to be having a problem with my thunderbolt to hdmi setup. I have macbook pro 2011-thunderbolt to hdmi-yamaha rxv571-lg tv setup. While playing a movie with the tv off my yamaha receiver shows the audio input to be 6 channel (5.1). When I turn the tv on, the input to my receiver switches to stereo 2.0. With my tv off i see the yamaha receiver in my midi audio setup and can correctly setup 5.1 audio. But when i turn the tv on, the yamaha disappears and the midi shows my LG tv with 2 channel audio and my yamaha shows an input of 2.0 instead of the 5.1 it gets with the tv off. Any help is greatly appreciated. I want 5.1 audio with my tv on, and the audio from my yamaha.