Aerial 5b and subs

I have been looking for a sub to put a little floor under my Aerial 5b monitors powered by Primare I30. I already have a B&W asw 608 which sounded quite okay but lacked power. I have tried the Velodyne HGS10/DD10 and was disappointed, it sounded heavy and not a good match for the Aerials. I am guessing that it has to do with the servo which seems to have an iron fisted mechanical quality. My thought over this disappointment is that a downfiring sub would interfere less with the sound signature of a monitor and that the REL approach is the way to go. My problem is the size of a Strata and am looking for suggestions in the foot cube range. Opinions on the Schweikert VRS1 or other options appreciated.