I have a RX-V663 in my bedroom running def tech speakers, and it sounds great. Even though my bedroom is small compared to most living room/home theater sized rooms, I have it calibrated to 75db at reference level, using the receivers internal tones, and it has no problems whatsoever getting very loud and still sounding great. Just yesterday I was playing some Pink Floyd and had the receiver in pure direct mode playing it for a few seconds at -5, so it was quite loud. However I have an old onkyo exteral 105 watts x 2 channel amp pusing it instead of the receiver, but it still did fine. I also set everything manually and didn't even mess with the YPAO since it gets things wrong half the time anyway, I think the only thing the YPAO is good for is room correction, if you want to use it for the Parametric EQ, which I don't like anyway.