Need recommendations for high gain/small footprint class d amplifier

I'm looking for a smaller sized class d amplifier to biamp the bass drivers in my custom speakers, which I was told should be about a 3 ohm load.  I'd say something with at least a nominal voltage gain over 30 dB should do.  My stereo rack was built for smaller components, mainly using Bel Canto and Red Dragon currently.  I can squeeze something up to 13.75 inches into the rack but a bit narrower would be easier to work with. I've been considering the Channel Islands D-500 but would like to keep it under a $1000 used if possible.  Your recommendations are appreciated.