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!