Best Home Theater Amp

What speakers are you using? That might help us to provide you with better suggestions. Also, any particular reason you feel the need to upgrade from the Lexicon - not enough power, not the sound you like, etc.?? Any interest in the LX series?

Anthem is one worth looking at. Their P5 and P2 (5-channel and 2-channel) are 325w/ch and should provide more power than you'll need unless you have very power hungry speakers. They also have the A5 and A2, but I'm not sure if you would consider those an upgrade from your Lexicon. Theta is certainly another company to consider.

I currently have the Piega P4 series of speakers, but I am looking for an amp that can carry me through for a number of years and handle my next speaker purchase (likely Revel or Aerial)

I would recommend the Proceed Hpa 2-3 They are both an audio bargin due to proceed going out of business.

I am very happy with my Classe CAV 500. Less than 5000$ on audiogon. Rated conservatively at 200wpc all channels driven. It is a 5 channel amp. RCA and Balanced. A lot better than my Sunfire cinema grand with similiar power ratings.

Yes, this is an incomplete question! It's like asking, "what is the best car part?", or "what is the best ingredient in a recipie". It's all dependent on the rest of the team, and personal preference, even system matching.
One "perfect" amp for one system might not be even a workable choice for another.