400W amp under $2000

The Hafler Transnova 9505 puts out 750W at 8ohms, in bridged mode, and is fully differential from input to output(unlike a lot of other amps). They are still supported by Rockford Fosgate, that actually built them. Fosgate bought the Hafler name a few years back. They have phenomenal slew rate and damping factors. Here's a link to the manual:(http://www.w1vd.com/9505manual.pdf) I've been using one for years with my woofers. It's given me wonderfully accurate, defined and extended bottom end.

I think a highly underated amp that is rated at 300 watts is the Innersound 300 ESL. I owned one and while I think the Parasound JC-1s sound better, the 300 ESL was very solid. It would be my immediate choice if I needed a less expensive high powered amp. They aren't made anymore and could probably be had for 1000 bucks or so.

PS Audio GCC 250 Gain Cell amp 500 wpc @ 4 ohms

BelCanto Ref1000's are 500W into 8ohms. You can find them on the used market for just above the $2k mark. They worked superbly well in my system, and I heard them in several of the systems at RMAF doing the same. YMMV. There are other class D amps that may fit your requirements as well (CIA, Nuforce, etc.) but I have no solid experience to recommend them or not.

Marco