Amp for Revel Gems

As a former owner of Ultima Gem, I would recommend two options. The easiest way seems to be following McIntosh way and buy power amp (stereo or mono) for C2200. Or try one of Mark Levinson amps, 436 for ex.
Good luck !

Odyssey Stratos?
http://www.odysseyaudio.com/products-stratos-mono.html

Trying to find a $50K investment that appreciates in value is no easy thing these days, so why not enjoy it on the way down :)

OTOH, I see a pair of Theta Citadels offered right now on Agon for $6895, which I expect would work very well, though they are a little over your budget.

Mark Levinson or Jeff Rowland, and of course higher-level McIntosh solid state amps all seem like good ideas as well. McIntosh and Revel seem to play well together.

Audio Research D400 MKII ??????

I highly recommend the new Mark Levinson 500H series amps. That's what I own powering my Revels.