superhonestben,i liked the mc252 so much that i went ahead & bought a 2nd mc252 & im running them as monoblocks with the c2200 preamp.
your thread got me wondering so i tried balanced against the rca inputs,there was a huge difference but my experience was the exact oposite,the xlr's not only produced a better & cleaner overall sound but my overall volume increased too with the xlr's.
the volume wasnt just increased either the xlr's raised the level where the amps began to klip,im leaving mine hooked up with xlr's from now on & im using cheapie xlr's too.
i wonder if eldartford called it right & there isnt somthing going on with your interconnects,a cheap way to try another set of xlr's is to go to your local guitar center & pick up a set,usually around $15 or $20 for a 3ft pair.
BTW,i love the mc252 c2200 combo,i went from a mc500 to running the 2 mc252's as monoblock's & im extremly satisfied as they are very musical amps with big balls too!
mike.