Class D recommendations for woofers in biamp set-up---size matters

Installing the last component in a custom cabinet that has a max shelf width of 13.75 inches and looking to replace my current woofer amp in a biamp set-up using something akin to Legacy Focus (clones) with 2 12" peerless 1259 woofers per side.  These aren't just doing subwoofing and cover well into the lower vocal frequencies so articulation is a must.  

My only experience with Class D so far was the original Wyred4Sound ST-500 (hated it) and now the Red Dragon S-500 (love it!).  What's excellent at lower to upper bass, is 13.75 inches wide at the most, and can be found on the used market for under $1000 (even less would be better)?   

The rest of the system is an Audio Alchemy DPA-1 with upgraded power supply and Revelation Audio umbilical, Red Dragon S500, a Kingrex PREference preamp controlling volume to the bass amps, all plugged into an Equi-Core 1800.  Thanks!
If you love the Red Dragon S500, you will adore the Legacy Audio i.V2 Ultra. I reviewed both the Red Dragon and Legacy (i.V4 Ultra) amps for 

The Legacy i.V Ultra is an extremely articulate amp. 
Hello Douglas,

     Thanks for the recommendation.  I've been a follower of yours for quite some time having purchased both the bridged Pathos Classic MK III and the Cambridge 840W.  Both were quite good.  The Legacy looks very interesting but the cost is an issue.  I am actually getting to the point of (hopefully) no further upgrades, at least for a good long while.  I just want to find a more suitable amp to drive the woofers in my speakers.  Thanks again!