I know that with HDMI you can do both audio and video. But to get the sound from the movie you connect the Blu ray to the sound system, right? And then that sound system, through HDMI wire, to the TV?
Is that how it's done?
Actually, why not hook up both the amp and the TV simultaneously? Any Blu-Ray player should have a separate audio out. My cheapo DVD does.
So the HDMI (with audio) goes to the TV, and the separate audio channel goes out to the amp. A digital audio connector (S/PDIF) should support 5.1.
You can also plug the TV into the amp, so you get whatever you're watching amplified (DVD, cable, playstation, whatever).
If you plug everything into the amp, you won't be able to watch TV and play music at the same time. Seems silly, but there's plenty of shows (sports, news) where you could have music on and not interfere with the show.