need good minimalist preamp or headphone amp to actively drive woofers in a biamp setup

I'm biamping a pair of custom speakers, kinda like a Legacy Focus clone using mostly Eton drivers.  I'm going directly from the source, either a Consonance Droplet 5.0 or a Raysonic 228, into a four channel Jaton amplifier.  The woofers are a little less efficient that the other drivers so the bass, from a quad of Peerless 1259 woofers, is not what one would expect or desire.  In the past, I've used either big integrated amps to drive the woofers or pro amps to good effect but I really like the bass from the Jaton amps.   So, I would like to add a minimalist preamp between the cdp and the amp driving the woofers.  I tried a Parasound ZPre II and it did the job but obliterated  fine details so I need something more revealing.  I'm considering the Morrison Elad but would like to hear other options.  I'd even consider a good headphone amp though I have absolutely no experience with them and I don't want to run the bass through another DAC as I really like the sound from either of my current cd players.  I'd like to spend around $500 or so for this project, no more than $1000 please on the used market.  Many thanks for helpful recommendations!