Noob receiver question

[rartist]

I have a old HT setup at home and would like to start upgrading it. My BR player is a PS3 and the sound for all that goes to an elderly Sony STR-DE445 on an optical. The rear left channel on that receiver is pretty much gone (sometimes I can jog it temporarily with LOUD sound levels, like the plane crash sequence in Fight Club), and I've though about trying to get it repaired, or use the $$ toward replacing it. The STR-DE445 has only the one optical connection I can use, the rest of it is useless.

If anyone could point me in a good direction to start. I wish I had gobs of money to throw at this, but I don't. I looked last night at bestbuy.com at some receivers ($400 neighborhood; a Sony 7.1 STR-DG820), but I don't understand 7.1 in relation to blu-ray and am just starting out. Receiver will come first, new speakers later on.