Map,
The little MBLs are funny animals. They're designed with a low end roll-off that is supposed to match certain characteristics of the MBL subwoofer, making them a tough match for other subwoofer brands (according to my local MBL dealer, anyway - so maybe a grain of salt should be added to that statement). I don't know if the MBL subs are available anymore (I didn't see any on the web site last I looked), so I'm not sure where the 121/newer versions fit these days. The 121s that I've heard (in a small to medium sized room) on a couple of occasions lacked bottom end power (surprise!) as a stand-alone and (IIRC) the MBL subs they were paired with were too much for the room (to my ear, as set up by that dealer, anyway).
The "in-between" floor standers (111,116) seem to be the better choices for medium sized rooms. However, like the 121, these do not feature the radial midrange driver of the 101. I thought that the 121 w/sub, the 116, and the 111 each sounded pretty good in its own way - and shared a definite "family resemblance" to each other. However, at the end of the day, the 101 strikes me as a fundamentally different (and much more fun) animal than the less expensive models in the MBL line.
Marty
Caveat: All observations from a couple of years back when I was seriously thinking about buying MBL speakers and auditioning the various models with some frequency. The model line-up has since changed a bit and I can't be sure that these observations are applicable to the current line.