I'm strictly running 2CH (stereo) - no HT. My M80's, especially driven by the RR2150, deliver a very balanced, natural, full sound that I'm quite pleased with - but I can't help but wonder if a touch of extra Low Freq might be nice for acoustic bass, etc.
I'd want something 'musical' vs 'Exploding Death Star Special fX' and especially something that would blend seamlessly with the M80s. I've had my eye on the Axiom EP400 but have a hard time justifying that price point for the little goose I'm after.
Room is 14' x18' (open on one of the 14' sides) with a 10-12" angled ceiling.
Carpet over concrete slab floor - popcorn ceiling.
Having never owned a proper sub - I would appreciate your thoughts?

M80:
http://www.axiomaudio.com/m80ti_main.html

EP400:
http://www.axiomaudio.com/ep400_main.html