Room treatments are always in the back of my mind but I'm still hesitant to go there. Until I do, I get far better "kick" or "punch" at a 40Hz cross-over while retaining the "soft" textures that most of us agree the 600 is wonderful at. BTW, I didn't feel these textures were missing with the 350V3; they were however a touch "harder" which I actually liked very much.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated