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

I reiterate: The tweeters in OP's speakers are either working properly or they are not.  And nobody here knows what other variables/factors are present in OP's situation. Not every problem nail needs a sledgehammer. (HUH? whatever does that mean?)

I suspect that @dekay  is on the right track.  

I will say it's (sorta) fun to read all the responses in this thread.  But I think it's time for me to unfollow. Best wishes and I hope OP gets it sorted out.

mozartfan would you put a cork in it?

ONCE again read before you post..

I offered a reasonable solution it see if the tweeter section is playing and if it is, let it break in.

Second a di pole will comb filter like no other it will cancel out front to rear because of the common pole.

PUT a pillow over the back of the tweeter section to stop the combing,. IF that works you know it’s combing. NOW position the speaker to reduce the combing as much as you can.. The -9db should go down. 

You can double check for combing by using only a single speaker, pull it to the center of the room..

TWO ears TWO eyes, ONE mouth... Order away, they are great speakers..

Regards

1.7i's sound like they have a head cold because of where the inductor is placed in the crossover. 

If you don't want to mess with the insides, the easy solution is to buy a Shiit Loki or Lokius and bump the frequency you are not hearing properly. I bought one as an amusement and not only does it do that well, but you can also bump the bass, as they will produce a significant amount more than their stock configuration. Same concept as a plate amp for subs. Box subs don't go that low naturally, their bass is intentionally overdriven. Not talking about open baffle or horn subs, just boxed ones.

Let the naysayers descend like rabid wild animals while they mic measure their rooms and let a computer do the tampering for them, all feeling safe on the streets knowing there are no tone controls on their preamps.

Everything else that offers a significant performance increase is major surgery that requires removing the panty hose, starting with a million staples.

williethe53b is Back!  "rabid wild animals?" WTF?

I had the LRS for a while and liked them so much I stepped up to the 1.7i

I find they would run OK on a 25 watt tube pre/power amp (Cary Audio), a 50 watt tube integrated (Jolida), but they shine with big SS power (Adcom GFA-365 mono-blocks).

They sound great to me.  Placement is five feet (5') from the front wall, tweeters out, toe-in to aim just outside your ears.

Past speakers in the same room were KEF 104/2, Infinity RS II, Klipsch Chorus II.

PS - I can't hear above 13kHz....................................