I am running old Crown PSA-2's (6 of them) with my 990. Balanced (or 1/4") inputs, adjustable gains, lots and lots of power. They are fan cooled, and so can be noisy (mine sit in an adjascent storage room), plus they'll throw off enough heat to noticably warm up my small theater room over a few hours. But all in all, I couldn't be happier with them.