The 3 amps that I recommended earlier are all integrateds...I haven't seen curves on the Infinity's, but I've heard the old Audio Refinement drive for ohms in the past with very good authority... Unless the Infinity's are straying into 2 ohm territory it should be good. Id the speaker stays in lower impedences below 4 ohms over any real frequency range, then no, I would not use it.
The Coda and the Krell both however would drive these speakers to any level that you would care to listen. I can't speak for others, but I wouldn't compare the Adcom with either of these integrateds.
When John at Musical Concepts Modifies an Adcom, he replaces the boards, they really are not Adcoms anymore. He adds a substantial cost to the 555 and you would still need a preamp.... All 3 integrateds that I recommended also have a remote.
Just trying to stress the points of why I suggested these...
if you want to go the power amp route. The 555 or 5500 will work fine, you could add a Sumo Andromeda II or III. Any of the Sumo or Adcom amps should run $400 to $600, but again, you'll need a preamp.