Which receivers have decent stereo performance?

Well if you can use the Yamaha as a preamp for now.I would use a seperate amp or amps for the Soliloquy 6.3s.The speakers are so efficient the Yamaha doesn't sense a load so it want put out any real power.
Two Monarchy SM-70 monoblocks used ($700) will give you an enormous improvement!Even a Van Alstine 120 D will take them to a different level.You can get some Acoustic Research directional interconnects from bestbuy.com for $13.00(shipping included).Parts numbers are AP0-30 or AP0-31..depending on lengths.Try to stay with the shorter lengths if you can. These interconnects do not know their place when it comes to price verses performance! Theres a Van Alstine 120D for sale on Audiogon right now! $450.00 plus some AR ICs will put you under $500.00 total and the improvements will be huge!

Trust me on this one you want be disappointed!
Good Luck!

No you want have too unplug anything.Run the interconnects from the preouts on back of the receiver to the inputs of the mono blocks.Take your speaker cables off the receiver and plug one into each amp . Your main speakers will receive the same signal as the rest of the speakers when watching movies.You are good to go!Take a pair of ICs and come out of your dvd player analog outputs into the analog inputs on the back of the yamaha(preferable your left and right inputs for six channel music).This will take the soundfield processing of the yamaha out of the equation.This will give you the best 2 channel sound using the reciever as a preamp.