Greetings!
I've have two of the 200s and I'm using them to power my fronts with my 750 powering the rears and center. I have Sonus Faber (Fronts - Concertos, Rears - COncertinos) speakers all the way around and they do better with more power. The fronts now really sound very full with this arrangement.
In listening to music, I've heard the greatest difference over the 750 and for HT, the rears suddenly came to life now that the 750 has fewer speakers to drive.
I have not heard any hiss or hum. Everything in my closet is driven from a dedicated 20 amp curcuit with power conditioning in front of the components.
The 200s are configured to turn on when sensing music until I can get to Radio Shack and get a couple of cables to trigger them. My Anthem AVM 20 has 2 low voltage triggers one turns on the 750 and the other will turn on the 200s in a daisy chain configuration. While in the music on mode, when you turn everything off, you do hear this low level rumble as the 200s power down. Not sure if this will go away when I change the triggers.