As rsf507 states, multiple subs tends to resolve node problems. Google "subwoofer swarm" for an explanation for why multiple subs are usually better than one.
Your reason for wanting to free your speakers from reproducing the lows, is one great reason for adding subs, Mids and midbass will improve noticeably.
What do you mean when you say you are not looking for 'more bass'?
I ask, because there is more ambient information in low bass than many people realize. Adding bass down to the lowest octave, opens up the soundstage.