Ideas For A Beefy Solid State Amp For Subwoofer Duties

Hey,

I'm trying some different things with my system and having another dabble with DSP for LF, basically a revamp of a failed 'Swarm' experiment.

I have 4 subs where I've pulled the plate amps and I want to drive each from either a pair of stereo amps or 4 monoblocks.
Two of the drivers are high excursion 15" drivers and two are 12" diameter. The 15" were driven by older 400w plate amps and the two 12" have newer Dayton-Audio 500w plate amps. I don't want to retain any of the plate amps (longer story).

I'd like to budget around $1500 - $2000 max for the amps for all 4 subs, and would likely purchase used.

I've looked at a few pro amps including the Crown XLS2502 2 Channel which puts out a healthy 775w / 4 ohms and actually has a reputation for very good sound quality. Two of those come in under budget.

Then I've looked at a couple options from Bel Canto, but they come in above budget at the power level required.
The original NuForce 9's can be had for under a grand a pair, but they're less than optimal in terms of power. Obviously the common thread here is finding amps with a high damping factor.

Any suggestions?
Thoughts on pro audio gear for this type of application?
Is Class D the way to go?

Main speakers are Dunlavy III driven by Thor 60w tube monos.

Cheers
Rooze