Sub for Acoustats 2+2

Most people here are going to recommend a REL sub. It integrates well with everything.

It all depends. Personally with my Acoustats and the music
I listen to, I have never needed a subwoofer. However, I
have tried a friend's Sunfire Sub. It integrated well
with the system and played rock and roll with authority.

I'm listening to my 2+2's with a pair of Muse 22's. Sounds very good (to me). Rock solid and good looking (like me, not...) Muse 18's have a card available for the speed issue as the Acoustats are relatively fast, and a slow sub will weird out the sound. IMHO.