Help finding a Mid-Sub

Look into the Wilson-Benesch Torus. A large 18" diaphragm that operates in push pull much like an electrostatic speaker. The white pages are here: http://wilson-benesch.com/downloads/whitepapers/Wilson_Benesch_Torus_White_Paper.pdf

What about the Hsu MBM-12 MkII?? It's a Mid Subwoofer that can be tuned for use with either a true sub or used by itself.

If its plate amp is not your thing, you may want to consider the possibility of modifying the sub to accept a better amp...

Mr. Pigchild.

There is a pair of the Torus Infrasonic Generators and a pair of the Torus amps/crossover for sale on audiogon. I wouldn't miss it.

See the thread "Slam what is it" and read martykyl response which describes what I want and what you might want as well. I don't want a sub that adds bottom end weight or muck, so that everything ends with a thud and a shudder. I want "kick" in my kick drum, a solid sound you can feel. The bass needs to be punchy and fast not heavy and slow.
The Gallo subs are sealed for quick transients and round so they are very rigid. They are compact and easy to maneuver. The controls are simple and intuitive for ease of setup. I use two of them in my winter setup and in another month I'll have them up and running again. Response in my room goes down to 25hz but what's really important is what happens in the 50-70hz range.
I really hated the REL sub, never achieved what I wanted. The REL is marketed as a "sub bass" system and that's not the sound of live music or what I wanted. I've had at least five other subs that never cut it either. For a measly 1200.00 per pair for the Gallo's you can't go wrong.

Check out the SVS line of subwoofers!