Thanks for the responses, 'goners.
To answer your questions:
-Tpreaves, yes - it'd be an easy thing to try.
-Nicotico, I suppose you could call my room sparsely furnished, but it does have heavy drapes behind the listening position, a carpeted area, chairs, etc. I've had smaller speakers work better (i.e., other Proacs, Spendor, Sonus Faber) but not provide the low end I seek. The best shot was a system comprised of a Graff integrated driving Proac D25, supplemented with an REL Strata III sub.
-Dopogue, I always tighten up the drivers when I buy a pair of speakers, but have neglected to do it this time around. I'm on it!
-Brf, Great idea. I'm a cyclist and drummer and have used the blue Locktite for a number of uses. I'll try it on the driver bolts.
Thanks to all!
-Bob R