Firstly since no one has asked - what do you think of the sound of the two amps with your speakers versus the ATI. ATI is no slouch actually and there will be no audible difference going from 350 watts to 400watts all else being the same.

High Damping factors come with high negative feed-back. UHF magazine - yes I know - recommends avoiding amplifiers with damping facors much higher the 40. But they are about home high end audio - not necessarily the real world. Before jumping on them for saying it e-mail them and get more of a reason why - they state this on 77 of their book.

Of course you are talking to a person who just heard a 9 watt Single Ended amp and walked away getting more deeper tight bass and more extended grain free highs than the Bryston 3BST could muster with the appropriate speaker. No mid range euphoic warmth, no noise, no hum, and played at soft or very loud levels with astounding macro and micro dynamics.

Granted you speaker may need more power - Crown? Post at http://www.audioasylum.com/forums/amp/bbs.html for some more takes on Crown.