Stephane, welcome. Of course your setup is far more than just "decent" and would appear to be greatly pleasing, including the bass. Please don't be offended by this suggestion(it's happened here on at least two occasions), but are you absolutely certain that the woofers on the 2.3s are actually operating? You mention biwiring, which raises a possibility(slim)that the woofers haven't been wired properly. Wire the woofer terminals alone to check this if it isn't clear at this point.
The point about the result with the sub not being as "natural" hasn't been my experience when using an appropriate crossover, generally 80Hz. Although you should be delighted with the M80s, there seems to be something in your present setup that may be incorrect and is preventing your full satisfaction.
