Which receivers have decent stereo performance?

Anthem or NAD.

Outlaw Audio RR2160 new here

If purchasing a used/vintage receiver, worn parts may need replacement meaning added costs and time.

While not a receiver in the traditional sense (it's a streaming integrated amp, with no AM/FM radio) the Marantz PM 7000N has far better than average SQ, and with its conservatively rated 60/90 W/ch amp power, it is capable of driving most speakers, and certainly the 90dB 1W/1m Soliloquy 6.3s, to greater than normal listening levels. I have used the PM7000N in my 2nd system for over 3 years and am overall very pleased with it. At nearly 25lbs, it is a solid piece, both physically and acoustically. 

For my HT system I went with the NAD 751 (now 752) specifically because of the excellence of its EARS two-channel to 5.1 decoder/synthesizer. Really great ambient feel from two channel sources! I often listen to high-quality FM from my computer chair opposite end of room, well past the surrounds, and the 5.1 mix is FAR better than the squished stereo mode otherwise. For $500 it does yeoman's service in an all-round HT system, but it's tuner section isn't quite up to the level of its best ones of the early 90s Monitor Series, alas. Preamp section's quieter, though. But that EARS programmer gets my daily bravo!

I'm doing exactly that with my Denon AVR4800: using a separate amp to drive my Martin Logan reQuests by running ICs from the pre-outs of the Denon to the inputs of the amp and then connecting the speakers off the back of the amp. Works GREAT.

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.

Instead of wasting money in a bigger receiver, the suggestion of a separate amp make marked impact in the performance of Soliloqys and will definetly set you square in the path of better sonics, in the future. I might call the purchase of the 1K receiver as a temporary solution, which in the long run will force you to squander more money in the selling and upgrading game. All receivers, used below 1K and the one you are using were built to fit an economic formula in the minds the company, a separate amplifier, as the Monarchy that were suggest has less compromise in their production than a mass produced receiver....and if there is a compromise, it was done accounting the clientele of the buyers who would purchase their amp....people who can be very demanding of the quality that the amp will produce. Simply, go for the amps.

If I follow Gmood1 advice, I need to unplug/plug the speaker cables when switching from stereo to HT from amp to receiver, right?

I'd second Gmood1 suggestion of adding an amp. I have the RX-v2200 and was not happy with the 2-channel sound either. My Paradigm Studio 60s are not very efficient and the Yamaha didn't have the umph to drive them. I added an Odyssey amp and was amazed at how much the lows and the mid-range opened up. Add the amp, not another receiver!

I would go with a Marantz or a denon. both are pretty good at music. A friend of mine have almost the same system set up, I have a Yamaha RX-V800, and he has a Marantz 7300. his sounds much better for music

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!