Ha - something I actually know something about on this site (yay maybe I can contribute/reciprocate)!
I also like Yamaha (use an early 90's and still awesome RX-V2090). Just get a Niles switcher and run it with all your various rooms off your "B" speaker input. About 100-150 bucks or so for 4 speaker switcher. Keep you main/surround (whatever) on your "A" and turn off the rest of the house ("B") when watching 5.1 movies, cranking serious hi-fi. You need to get "in wall" rated wire if you want to be "to code". Soundstream makes very resonably priced wire you can buy by the foot at high end places. I wouldn't worry too much about the gage (I spent over 800bucks on the rest of the wiring Monster, Soundstream, "oxygen free copper" something etc, etc so I am def a believer in good wire....but for aux speakers not that much diff...just saying....
On "speaker A", I use Paradigm speakers, 2 main, 2 surround, 1 center, and w/ sub (not crazy $ and sound fantastic...I highly recommend them...and over the years I have heard/have friends with giant $$ Mac stuff, Nak, B&O, Klipsch, B&W, Dalquist, yadayada and EVERYBODY loves the paradigms.
On the "speaker B", through the Niles, I run my old ADS 780s in basement fireplace area, another pair of small Paradigms (Titans...really great) in basement bar, and 2 sets of Minimus 7s on two outdoor decks. The receiver can drive all of it at the same time. Quite loud. No problems.
Different inputs at same time....well I got nothing on that one. Also, X10 paramid remote relay is worth a look if they still make it. Pretty cool to be out on the deck or basement with your remote(s) and control the reciever/DVD/CD etc that is sitting in your living room.
One more thing, if your gonna buy something new, Yamaha / HK / Denon / Pioneer (prob more) all make really good stuff. But they also make wimpy stuff. Rule of thumb: plan to spend at least $1K (any brand) if you want an up-to-date AND kickass in terms of power reciever. Otherwise, save your money and wait.
Hope this helps you.