I does sound to me like you're having some trouble adjusting to the new sound. But from your descripion of the sound, it does also sounds like you prefer a more detailed speaker. From what I've read on these boards, the M40 and M50 speakers (as well as the M3) are Axioms most "laid back" sounding speakers.
If I were you, before I gave up on Axiom, I would try one of two things.
1) (and this would be what I would do) Try out the M22ti paired with a Hsu VTF-2 subwoofer. Your living room is indeed not all that large. You can easily fill that room with a pair of M22's. The added Hsu will fill in the low end, with much better bass than you'll ever get from a tower speaker.
2) Try the M60ti's. They will give you more low end (not as much as adding a good sub), but they will also have much more detail in the highs than the M50's.
From what you've described, I think you'll be much happier with either of these options than you are with the M50's alone.
