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


First time Magnepan owner - 5  days old 100+ burn-in hours on them
Associated Equipment:
-Denafrips Terminator Plus
-Holo Audio May KTE version
-Pass Labs X22 Pre-amp
-PrimaLuna EVO 400 Pre-amp
-Pass Labs XA100.8 Monos
-PrimaLuna EVO 400 Monos
-AntiCables interconnects and speaker cables
-Stock tweeter attenuator jumper replaced with AntiCables level 5 spade jumpers on the 1.7i's

My spectrum analyzer indicates both speakers highs are falling off beginning at 1.25K and are 9db down from 2.5K on
Been playing around with speaker placement and room treatments for 2 days now without any remediation. What am I missing? Suggestions appreciated.
128x128nayls02
Maggies are very sensitive to positioning.  You might try them with the tweeters on the inside and tilted towards you.  Just put CD cases behind the back legs.  Make sure they are several feet from the rear wall and try various angles.  But in general, you shouldn't be seeing that kind of rolloff on the top end so it is possible something is defective with the tweeters.
Have you checked the working of your spectrum analyser with different speakers?
Agreed with a few others,try the stock jumper. 
I use stock Maggie 1.7i, PrimaLuna tube preamp, SS Bel Canto monoblocks, and highs sound great. (Have not, however, done a freq analysis) 
The question is did you listen to these before purchasing them, and, if you did, what kind of electronics were used.  Also, what kind of speakers did you have before?  My take is that the somewhat soft PrimaLuna, combined with the somewhat soft Maggies and a possibly unfriendly acoustic in your room is possibly the problem.

Maggies aren't for precision at all and by all possible means useless for studios. Their design is reflection of engineering, science and experimenting, but not accuracy by very far.