I have two US Amps XT1600.4s 50x4 @ 4ohm, 100x4 @ 2ohm and 200x2 @ 2ohm. Also have a XT800.2 50x2 @4, 100x2 @ 2, 400x1 @ 4ohm.
Also have a used AX5600 5channel (underrated at 75x4 @ 4ohm + 500x1 @1ohm for the sub). But, I would say it needs minor repair. You could send it in to US Amps or repair yourself. The RCA inputs got pulled out of the amp by my 4ch RCAs and they aren't in as well as they should be. I would solder them in, or have US Amps repair it, but it does work at the moment. That's the only problem with it other than some scratches on the heat sink. See my threads for more info (in my sig). I was asking $100 shipped for each of the US Amps XTs, $285 for all 3.