Check out the system manufactured by Audiokinesis and the posts by Duke over on the Maggie forum at AA. He posts here as well (nice guy... I talked to him for about an hour on the phone one day about planar speaker choices).
A number of Maggie 1.6 owners have had good success with this system, which uses a number of subwoofers scattered about your room, driven off a single plate amp. Some interesting white papers on the theory, and some satisfied owners too.
It's on my Christmas list, so it's top of mind.
Other good choices are the REL Storm & Strata which are often seen here, or the Vandersteen 2Wq subs which use smaller woofer cones and are "fast" enough to be able to mesh. The Vandersteens also allow you to tune the "q" of the woofer to get a nice match, and they use speaker-level inputs, as do the REL, to carry the voicing of the amp to the subs as well to match your main speakers.
I've been using the Vandie, but in my current room, with actively bi-amped Maggies and Mye stands, my bass is strong enough that I rarely feel the need.
For some kinds of music, the solid foundation of a sub really is nice. But you might be surprised at how much bass you can extract from the 1.6's without having to add a sub or two (or four as Duke does). Be sure you've exhausted the other options (like placement and room treatments, such as Roomtunes) before you rush out and buy a sub. Most rooms have issues in the bass, and the sub can simply exacerbate them.
I've had my 1.6's in three different rooms, with wildly varying results. You should definitely experiment a lot before throwing money at the problem (don't ask me how I know this-- )
HTH
Frank
