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
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....................................
Sounds strange. I bought my pair of 1.7i's about 2 years ago with never have seen or listened to a Magnepan in my life. I figured for that low dough it was worth taking a chance. Hooked them up to my Primaluna Dialogue Premium HP Integrated amp with KT-150'S and was blown away by the sound! Plenty of highs and mids. I also use AntiCable speaker wire and the stock jumpers. I run two subs from the single out on the Primaluna. Blows away the Vandersteen 3A Signatures that I replaced. Dana
All Magnepan speakers require a lively back wall to generate the proper sound at the listening position. If the back wall is too damped, it will muffle the high frequencies. Remove any damping panels, foam, etc from behind the speakers and listen. Maggies do not respond well to rooms extensively treated for cone speakers.
Hello nayls02 . Check the fuses on the lower part of the rear of the panels. Replace them with 1 or 2 amp fast blow fuses, preferably ceramic.