Need help choosing a power amp

Look for the Bryston 3B - 4B - or 7B series amplifiers. All come with a 20 yr warranty and will be in the price range you desire.

If you are picking up Revel Concerta M12 speakers I would not go for Odyssey or Musical Fidelity. I still have a Adcom 545 in my home studio. I have owned the Odyssey and my bro-in-law owns MF stuff. Both of these will be too bright for those speakers, although they are both excellent amps, but not for your setup. I would get a warmer sounding amp like a used CJ MF series, The McCormack stuff, Classe, even the newer Adcom 5802 will sound much better and warmer. All of this stuff can be found used under $1K. Any of these amps will be a BIG leap over the Adcom 555MkII (and my Dad owned that one)!

Not to sound like a saleman, I will be selling my CJ MF-200 soon on Audiogon, and that would work for you also.

I've owned a number of amps. The two for under 2K that I'd recommend to anyone are the Audio Research 100.2, for around $1650 used, and the Classe CA-101, around $850 used. They're both robust 100 W/channel solid-state stereo amps with clean, engaging sound. More money does not, I've discovered the hard way, necessarily mean better sound. Classe's 101 is just a much better amp in most ways than their larger and 3-times-more-expensive 301.
And the ARC is almost the best I've ever owned. It bettered my old Classe Delta CA-2200 in many ways, though the Classe amp was a bit more evenly-balanced.

If you see a Forte 4a, that's a fantastic little amp and a steal at anywhere under $650. You could pay multiples more and not equal the sound of a 4a.

One I've not heard but about which sonnets have been written is the Pass Aleph 3. Maybe worth a listen.

happy hunting

Another option is to modify your existing Adcom. www.musicaldesign.com does just this. I have had a modified original 555 Adcom in my system going on 20 years now and trust me it does not sound like the stock unit. For under a grand it would be brought to a new level of performance. In fact I'm thinking of sending mine in for the Blackgate caps everyone is singing praises about. If you do modify you always want to go with the top level mods because you will sit there listening to music going wonder what it would have sounded like if I had the Blackgates or schotsky diodes put in it.
Trust your ears...

Well put Qdrone, it may be interesting to note that I lived with with the GFA-555 MKII longer than any other power amp since. Everyone that heard it liked it a great deal. At the time I thought this amp was the best, regardless of price. Only when I started to upgrade did I realize that the 555 MKII lacked in refinements and a large 3D soundstage. (This equation could be improved upon with the addition of a good tube preamp). It will always be a part of my past where I enjoyed listening to my music a great deal. I agree that this power amp could benefit tremendously from upgrades. Anyhow, jgreene is correct in regards to the ARC 100.2, a superp amplifier!