Lets look at your room first, while it's large in size (thats good) it has two dimensions (24') which are the same (thats bad), in your case it means that all bass modes from around 23hz. up to 300hz. range will be excited by both walls at the same frequency, this can cause bass notes to boom and loose focus. You may want to do some reading on room acoustics and room treatments, there is a new forum hosted by Rives over at the audio asylum web site on room acoustics, also plenty of other info. on the web to read. Because your room is large I would use it's size to your advantage, large rooms offer a much wider range of speaker/listener placement than do small rooms. Also types of speaker choices are much broader do to less constraints on placements. I'm going to go with an all Vmps speaker system for your room that will not be to hard for your Yamaha to drive to high spl's in your room, all speakers are at least 90db. efficient and 4ohm rated but can be orderd as 8ohm., all speakers can reach very high spl's, all speakers can go down to at least 45hz, all speakers use ribbons for mids and highs for a smooth seemless blend and will match well with any state of the art amps/preamps if you should decide to upgrade your gear to tube or solid state down the road for even better performance.
Main speakers:Vmps ribbon monitor 2's
-3db@22hz. with megawoofer upgrade-$2,850
Center speaker:Vmps large Ribbon Center (LRC)
Rear speakers:QSO-626R (ribbon monitor)
Rear speaker stands:$300
stands of your choice
This system can be had in your price range from more than one Vmps dealer who frequent the Vmps forum at audiocircle.com.
This system could also be scaled down a bit on the center and main speakers for less cost and still be very good, I brought you in at the price of $5,000 with max. performance and no subwoofer needed for high impact but could be added later. A scaled down system would require at least 1 sub. Hope I could be of some help, Enjoy the ride.