My New Magnepan 1.7i's sound dull and lifeless on the top end...why?

One difference between open baffle dipoles (such as planars) and dynamic drivers in enclosures (whether sealed or ported) is that dipoles "move" air from one side of the planar to the other---leaving the air pressure inside the room unaffected, while box speakers change the air pressure inside the room (and inside the enclosure, which is why the suspensions of drivers intended for use in enclosures differs from that intended for open baffle use).

@kingbarbuda, did you mean to say "percussiveness" rather than "persuasiveness"? If so, I find the bass panels of the big Maggies to have a very percussive sound, which is why they reproduce piano and drums so well. But that’s more a mid-bass rather than deep-bass (40Hz and down) phenomenon. Magnepan has been working on a dipole woofer system for a few years now, which uses multiple dynamic drivers in a sealed enclosure. It will be available as an add-on for current Magnepan models, and as the woofer system for a new model: the 30.7 For Condos.

Eminent Technology already offers such a woofer system, and then there is the state-of-the-art OB/Dipole Sub from Rythmik Audio/GR Research.

Not to be argumentative, but Maggies are NOT ribbon loudspeakers. Well, the tweeter in the 3.7i, 20.7i, and 30.7 is a ribbon driver, but all the rest of the Maggie line and all their drivers are planar-magnetics, not ribbons. A "ribbon" driver is a very specific thing (the diaphragm of the driver and the conductor that causes it to move are one in the same), not just any ol’ planar.

Calling Maggies a ribbon loudspeaker is like calling an electric bass a bass "guitar". Common (Steve Guttenberg regularly refers to Maggies as ribbons, and John Atkinson always calls his electric bass a bass guitar), and incorrect. ;-)