I picked up an ACI force sub, and absolutely love it. It is very fast and tight. I have AP sparks, which are fast speakers, and I cross over at 65hz, and this sub disappears into the soundstage. Kick drums are dead center and deep on rock & roll. This sub sounds like it is exactly what you are looking for. There are two crossover filters and a variable phase pot. Takes a little time to set up but well worth the effort. Hope this helps.
Subs for Magnepan 2.7's
I'm looking for a nice pair of subs that would match well with my speakers. Am considering ACI Forces, used RELs or James and the B&W PV-1s. Any suggestions would be appreciated. The use would mainly be for music and want a musical sub with deep,tight bass. I think a sealed (non ported) sub would be best. Thanks