subwoofers. they will work well, even w/full-range speakers. they will allow you to place your main speakers optimally for image & soundstage w/o regard to bass response - use the sub(s) for that. my subs were effective even w/my old thiel 3.5's, which were rated -2db @ 20hz. passive subs (i like vmps) an active x-over like a marchand xm-9, will allow for a seamless blend w/most any monitor, full-range or otherwise...
one caveat - your room may perhaps be a bit small for a truly full-range speaker, & even optimally locating a sub may not help. i also suggest you look into some sound-treatment, like tube-traps, etc...
doug s.