Magnepan MMG or something else

I would suggest that if you are adding a sub,get two.Many will argue that only one is needed,but the other will add more separation and more uniformly load the bass.Akin to a true full-range set of speakers.I don't believe the claims of non-directional bass below 100Hz-there are left-center-right ambience cues in the low frequencies.

I had MG12's in my 13 x 14' room and I initially drove them with a modded Dynaco ST 70. Excellent sound. I wanted more power and detail and I purchased a Moscode 300 and AVA Super PAS3i (VA design not Dyna) and the results were excellent The MG12's opened up and the sound was better than I ever imagined. The MG12's were about 41" from the back wall and 22 inches from the side wall. So the speakers were nearly in the middle of the room. Not good! But once I hit that sweet spot that wonderful midrange tight bass along with sweet and smooth highs made me smile. I had several audiophile friends tell me it didn't get much better than that.
I then added 1 Dali Suite 12" acoustic suspension model 1.2 subwoofer. This gave me more and a deeper soundstage. This cleard the bottom end up tremendously,I didn't have to deal with boomy bass. Shortly afterwards I bought a 2nd Dali Suite 1.2 sub and I was in hog heaven. You couldn't pry the Maggies from my room until one day I need more space in my room My listening room was now my office and I needed more space. I purchased a pair of Spica TC 60's to compare to the Maggies. They were so close in the it's presentation of sound but the power with the Maggies was better. I contacted JB (designer of the Spica speakers) and he assisted me in setting them up. Once that was done things were pretty even and the Spicas gave me much more space than the MG12's. I ended up keeping the TC60's and space limitations were the reason. The Maggies were more extended on top but with the right wire they were wonderful. I ended up with Vampire Wire 12 gauge hookup wire for the speakers. My Spicas are Tri Wired and gave me additional refinement and depth in my little room.

With that said the Maggies simply played louder and with more power but the TC 60s are only the length of a wire behind them. But they don't require a big beefy amp and that had alot to do with my decision. I added a VTL ST 85 to the system and it's sweet.

I have 3.6's, and had the MMG in the same room. Spring for the difference, get the 3.6, it is better in every way except price. The MMG was too small sounding and not detailed like the 3.6.

I had a Fiat 500 in my garage, not nearly as good as my Ferrari though both made in Italy.

Maggies sound is very sensitive to placement in the room and where you listen from accordingly. Have you tried tweaking the placement for best sound at you prime listening position? There are lots of possibilities on how to place MAggies that can have a big effect on their overall musicality.

Most good mmg setups I have heard are strong on musicality and micro-dynamics but weaker on bass and large scale dynamics. Could large scale dynamics be the aspect of "musicality" that is not happening?

If mmgs alone are scoring with bass levels but not musicality, that could well be a setup problem.

Regarding macro-dynamics/slam, if that is the issue, the common solution worth a try is to add a sub.

IF all this fails, then it might be time to move on but I would do whatever might be possible to max out performance of what you have first before making that decision.

Were you to move on, I would recommend a decent pair of Dynaudio monitors might be a good option. I also like OHM Walsh speakers in that they have a lot of planar-like musical traits but also excellent dynamics overall.