I've had good luck with an older Velodyne with my Maggie 2.7's - the F-1000. It has a 10 inch woofer that is quite fast. If you don't have an electronic crossover, you run the Maggies full range and run the Velodyne off the preamp outputs, and then crossover the Velodyne very low - I found around 38 Hz worked best in my room. You want a subwoofer that is fast (like the Rel, too), which you need to keep up with the Maggies.
Maggies and subwoofers
I have a pair of Maggie 3.6 speakers. Has anyone found a good subwoofer to mate up with these? I'm considering two Vandersteens or 1 Revel B-15. I'd sure like to hear other peoples experiences, choices, or experiences. Thanks.