Usual suspects for amplifiers are Emotiva(with some caution), Outlaw Audio, Anthem, Bryston, Axiom's own amps(used?). There is a myriad of used amps on the market. What I have been doing is checking out what is available used and then look to user reviews for quality concerns. AVS is a good source of people comlaining about this and that, you just have to sort through the minor complaints to find those that are valid.
I have hesitated on a coupls of used ones and missed out. Jakeman recommended a Sherbourn multichannel he saw and I waited a few days - too late.