best way to amplify seperate woofers?

I am pursing my first attempt at a 4-piece (2-channel) speaker system with seperate tweeter/mid enclosures and woofer enclosures. Two SEAS 8" woofers. I have a Vincent solid state 50 watt/channel (80 max) integrated amp with pre-outs (no main-in). I am not considering a large power amp to drive all 4 pieces as there is no point to pursuing seperates in that scenario. I know I could get a power amp (with a gain control)just for the woofers, but loose all the benefits of my last option. I like the idea of a stereo(dual mono) sub amp component in one chassis which has adjustable crossover and phasing. I see that there are offerings from Niles, Sonance, Klipsch, Polk, Velodyne, Boston Acoustics, and Anthony Gallo. Most of these have some kind of draw back, be that lack of wattage,combining both channels, or lack of controls except for the Gallo. This speaker system has a MSRP of around $7500, so I am not willing to compromise. Does anyone have any real world experience with this application? Can you make any manufacturer recommendations?
Do you want to play with solid state on the woofers and tubes on the mid/highs;any interest in this method?
I'm doing it right now w a pair of Ref 3A Supremas, but have just begun experimenting. I did a lot of searching and encountered some of the problems you noted. I eventually pulled on the trigger on the NHT active x-over driven from my tube pre-amp, w a Solid state 100 wpc amp driving the passive sub-woofers (also 2, 8" per side, iso-baric loading). This tawo box solution takes care of 50 hz down. VERY solid, non-boomy, stereo bass. The upper frequency box (actually a stand-alone Ref 3A Royal Master monitor which has an 8" nearly full range carbon fiber driver and a small fabric dome tweeter w a cap and resistor filter) is reflex loaded handling 40 hz and up. The high pass output from the active x-over feeds an EL-34 p-p amp and the monitor is bi-wired, since it has no real crossover. So far I am pretty happy w it. Another 2 box solution is the mono NHT subwoofer amp/x-over, one for each channel. The NHTs have lots of adjustability for x-over freq and phase, XLR and RCA ins and outs, gain, etc.