Wow this must be a real popular combo. I have the M22/VP100/QS4 as well and love it. And I haven't even had a chance to properly calibrate everything. I decided on the HSU VTF-2 instead of an Axiom sub (no offense guys). That is a monster of a sub. Someone recommended the HSU STF-2 which you can get (if you can find it) for $399 at CompUSA. But you can get the VTF-2 directly from HSU for $449 with free shipping right now. Main difference is you can tune the VTF-2 for either louder or lower bass, depending on if you use the port plug or not. The STF-2 is not tuneable, but is fixed to play down to 25hz. Either one would be a good choice.
