I am using a set of GR Research OB subs with custom speakers utilizing Altec Lancing 288/287 Field Coil Compression Horns that go from 400hz up and a set of Jamboree Bass Bins that go from 400HZ down to about 38hz. I cross the OB subs at about 60hz. sound is absolutely sublime
I am rebuilding the crossovers for the horns with parts from Danny. While the main rig is down, I am using the same subs with a set of Omega SHO Alnico monitors. I cross those at about 120HZ. Again fantastic sound. Not quite the Altecs but they don't weigh 300# each.
The OB subs load a room in such way that I think you can use them with just about anything.
Life is good