Help finding a subwoofer

I've said it before in this forum and I'll say it again, REL subs seem to be the one type of audio gear that almost everyone can agree on as being well built, having excellent performance, and a good value. In fact, I don't think I've seen a negative comment yet about an REL sub, although one person didn't care for the customer service.

What’s your budget?  Incidentally, I don’t know if you can use onboard DSP if you use high-level inputs. 

+1 @winnardt about REL quality and sound.

As to the high pass filter @dynamiclinearity I agree there are pros and cons. Full range speakers and good amplification can handle full signal.

The quality of the high pass filter is hugely important in a resolving system, and I believe in not altering (DSP etc) the signal. It adds distortion. That's just my approach.  DSP for a sub? may be a good idea to tune to eliminate room nodes.  I was able to move my two REL subs around until I had minimal bass booming.  The addition of ASC bass traps (I found them used here) in the corners smoothed it all out.  Who knows, if I had subs with iphone controlled DSP I would have liked that, but I think in the end I prefer the purity of the signal.

I was using a set of SEAS Froy3 speakers and added a pair of 18" woofers crossed passively about 85 Hz designed by the SEAS designer(a friend) and the improvement in openness , detail and clarity was overtly noticeable even thoughthe Froy3 was already very good. Of course being designed by the Froy3 designer the crossover between the speakers and woofers was custom designed for just this case.

I do understand the lack of a high pass when the high pass is generic and not a special design for the speakers and woofer. It's easier to integrate without the high pass but you pay a price for this flexibility.

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 ..."