Best Subwoofers? for my system

What are the best subwoofers to use with my system? I want to use two subs. My fronts are Aerial 7B's, center is Aerial CC3B. As soon as funds allow, I will be adding another set of 7B's for surrounds (& later another set for side surrounds).

I want something musical even if it doesn't have that last bit of impact when watching movies. I have heard very good things about REL & also the Aerial SW-12 sub.

Present System
Amps - (2) KAV-250a's & (1) KAV250a/3
Processor - Krell HTS (will be changing, Lexicon? Theta?)
DVD - Temporarily a "mid-fi" Pioneer (will also change)
CD - Classe CDP-1

Thanks in advance for your suggestions.