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

Either the tweeters on OP’s speakers are working properly or they’re not.

I say the following based on my decades of experience with Magnepan speakers. Amps, room, placement, source material, cables, fuses, the alignment of the stars, and so forth, and so on, have only had relatively minor, not dramatic effects on how the tweeters sound.

Whether I’ve used beefy tube mono amplification, a not-so-beefy tube integrated, a moderately-beefy hybrid integrated, or robust solid-state integrated, I find that I want to tame the tweeters a bit using resistors. The rest is refinement.

That is all.

Any tech who says no to Maggie's unless you have a very low watt amp isn't worth listening to. Maggie's may need subs for lack of the very low end but they sure don't lack high end sizzle unless something is wrong with your tweeter. They come with the jumpers or resistors to tame the highs in a lively room. Your tech probably doesn't sell Maggie's so is pushing something else which I doubt will ever match a Maggie for the $$.

I had 7 years with Maggie 3.7 s.  Preamp isn’t the issue. I had a nakamichi amp heavily biased to class a and it was a total mismatch.  Look for a a used Bryston or Mcormick  amp, or a modern parasound amp.  Needs an amp that can deliver fast settling amperage 

Suspect that they are not propely hooked up/connected.

If damaged it's unusual that both speakers would have the same fault.

Not a clue as to what the "add-ons" mentioned by the OP are, but suggest hooking them up stock (nasty jumper plate and all).

I responded to another Maggie owner here with similar complaints and the HF problem was resolved with proper hookup (poor electrical contact was the culprit I think, but too lazy to look back through my posts).

DeKay

 amp, or a modern parasound amp.  Needs an amp that can deliver fast settling amperage


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This is what my tech was getting at. 
~~Requires high(er) current~~ than what the Defy7 can deliver = Not a  match made in heaven.
Is what he was trying to express.
He suggests , sure for string quartet, the Magnepan + Defy marraige would be excellent..
Well thats not what was the intention. The magnepan was for voicing full slam orchestra, in super high definition rock solid bass, rich detailed perfect voiced midrange, and the most glorious highs ever heard by the human ear..
Is what I had set my hopes on for the Defy7.

Magnepan is quite magical, we all know this based on countless testimonials. 
The caveat is a  amplification current that can deliver the goods.
Lets stay focused. 

As I  now recall was often mentioned when discussing panels wayyy back in my Topic, ShootOut at the OK Corral...
How could i foget,,,which is why i never reconsidered going anything **panel*