@nymarty I am using a Devialet 400. It has high and low pass filters along with time delay. I have a Dayton Audio SA1000 as my subwoofer amp with second order and fourth order high and low pass filters, respectively, at 80Hz but I am not currently using these. I would if I were to go with separates or an integrated with a tape monitor. I'd lose the time delay feature of the Devialet but would hopefully make up for it with other attributes. I could also use a miniDSP or equivalent which you might consider as well.
@lonemountain Do the small speakers you measured have considerable bass output? I would guess that a speaker that goes to 50Hz would yield less of a gain than one that goes to 35Hz.