Thought I would add my worthless 2 pennies here...
I have a Pioneer Elite 81, only does switching, no upscaling.. I didn't want that, with the hit and miss reports on that, and the up and coming change over to newer better processors for upscaling, I was waiting. As well as my Panasonic Pro 50" plasma is only 1080i.
Well anyways I have a Yamaha DVD/Divx, Dish Network HD, and XBOX hooked up to the reciever going out to the Panasonic with absolutely no issues at all.
I am upconverting the xbox to HDMI and that works great too.
Works so nicely I am extremly thrilled that I haven't had any issues at all, just seemless install, and Picture is spectacular for me.
Sorry your having troubles, just thought I would share my equipment list and hookup scenario with you if it helps.
Warp