Originally Posted by fish5225
My room is 50x50 with a 30 ft sloped ceiling for most of the room.
Wow that's a huge space! It's so huge that assumptions about small room acoustics really don't hold. I hope you buy a measurement mike and post listening position measurements, because I'm genuinely curious to see where the modal region starts in a room that size.
Your Yamaha AVR should have enough grunt. If not, you'll probably need an amp with at least 3dBW more continuous. That's 300+ Watts. Anything less is just a waste of money and less energy efficient than using the amps in your AVR. (There are people who will tell you that "AVR Watts" are somehow not as good as "separate amp Watts." Usually in the course of either trying to sell you something or to justify their own purchaseWords for such people include con-man, scammer, charlatan, deaf idiot, etc.)
Another consideration you'll have with efficient speakers is that separate amps are often noisier than circuits integrated into an AVR, because the AVR will have gain structure internally optimized. IMO an amp with enough power to make a difference AND with a sufficiently high S/N ratio for such efficient speakers will be expensive. Think ATI AT6000, Anthem Statement, etc.
In that size space, you may actually do best with single a huge sub in a corner, with massive power. I don't know commercial subs well, and it depends of course on how big you can fit. (Here custom may be better than off-the-shelf, because it's easier to eke out all of the available space in a custom design.
Also, you should likely probably keep your mains crossover pretty low, like somewhere around 50-60Hz.