I also thought that the LCR3 would have been the top of the line, I'm no audiophile, but everyone seems to agree that the MTM design is not designed well, and there is a lack of extension in the RC-1 and very little movement.
I believe the larger size of the P6's mid-woof has a lot to do with the added bass, i could add my unproven and highly uneducated reasoning, such as the port being possibly to small for the size of the speakers.
I will say that in my opinion the speakers have amazing clarity and seperation, i was watching Steve Vai, Visual Studio Theories DVD with full orchestra, and being able to pick out the flutes and bells, over the much more pronounced trumpets and trombones was a true pleasure to listen to.
Though i do agree that a sub is needed, i do have them crossed over at 80hz, rather then the lower 60 or 40hz, though they will handle the lower cross over at moderate volume, though the RC-1 doesn't handle it as well as the P6's do.