Help finding a subwoofer

I believe in not altering (DSP etc) the signal. It adds distortion.

No it doesn't. CD digital output into a DSP offers the ability to exactly tailor the XO frequency and slope to match the drivers, something that is extremely difficult with passive XO. Additional benefits are minimum phase, time alignment, room correction and precise driver control as damping factor is preserved at Fxo instead of being ZERO with a passive XO.

99% have never heard a correctly timed, phased and crossed-over multi-amp system. Shock and awe are the usual reactions when they do. Poorly recorded multi-mic compressed one dimensional recordings are exposed as the dreck they are. Comments like "That's one of my favorite recordings and it sounds so lifeless compared to ..." 

Thank you for those great responses.

Ieales do you mind to elaborate on what you meant when you wrote preserving the damping factor at crossover frequency if that is what you mean with Fxo 

I want to spend 1500 us used in two subs.

I am curious about the Martin Logan Dynamo 1000 which are on eBay for 900 a piece. I own a pair of tiny Motion 15 speakers and think that Martin Logan know their business. Talking about speakers I have Cain and Cain Single Ben with Fostex 8 in. 97 db eff drivers. Want to spend about 3000 in a good tube amp 35 watt… the high level input I envision to be able to follow the tube amp signal better.I see SVS is VERY popular so I am curious about the micro 3000 but if other models have remote management that is another thing!,,,,,