Yup. Old skool RCA is only for stereo, 2 channels.
U7 does not support optical.
However, it supports coaxial (SPIDIF connector), and provided your HT system accepts this as well.
There are optical-coaxial/vice-versa converter available if you need those.
If your HT does not have any coax/optical at all, the U7 supports analog 5.1 out as well. They're marked centre, side, rear. HT needs to support these too.
Maybe it'll help if you describe you HT system. Is it a standalone amp or those all-in-one HT with speakers and BD player?
If it's an Amp that supports HDMI in, I'd recommend that instead. Audio/Video through one cable. Don't even need the U7 for that.
EDIT: Darn.. magix beat me to it while I was typing.. haha
