Also, I don't think optical passes 7.1, just up to 5.1. Someone may need to correct me here.
I have a 6.1 receiver. I use the optical output from the PS3. I have seen some 6.1 content off of some of my Blu-ray discs. I can't remember which ones off hand. My receiver auto detects between DTS and DD, 5.1 and 6.1