I suspect that this has to do with HDMI hand-shaking and display determination. Whenever the source (i.e. bluray / satellite) is connected, it sends a display question all the way through the HDMI cable chain. The display/TV then reports back it's display type and the resolutions/rates it can display. The source device then will send acceptable audio and video. When your TV is off, there is no display device. In this situation, the source may be defaulting to the lowest acceptable rate for audio, which is typically 2-channel PCM.