Interesting question. Not surprisingly, a lot of 990\'s seem to end up paired up with Outlaw amps (combo pricing may have something to do with that), but other amps do seem to get mentioned around here. ATI, Parasound, Adcom, and Rotel are probably the most common non-Outlaw amps. There are a number of other brands represented in the speakers/amps thread (see my link above), including Bryston, Odyssey, and Sunfire to name a few, and even at least one person in that thread running Mackie powered monitors. I don't recall hearing of any "problem child" combinations of 990 and amp yet, but will be curious to see what thoughts crop up here.