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

Thank you for the responses. 
- Using an EQ does help, but introduces it's own set of undesirealbe sonic characteristics.
- I would hope my Pass Labs gear would be considered good SS...yet still unacceptable in the high frequencies, and only marginally better than the Prima Luna gear on the 1.7i's.
- I have a pair of LRS's who's high frequencies are vastly superior to the 1.7i's??
- Swapped out the AntiCables with some Canare interconnects and Mogami speaker cables...sounded worse.
- I've tried all the settings variations on the PrimaLuna's 8, 4, and 2 ohm, and high & low bias.

The funny/bonus thing is the harsh poorly recorded music sounds better than any of my reference audiophile recordings on the 1.7i's. I may keep them just for that gem of an attribute.

Have you tried using the stock u-shaped jumper in place of your anticables attenuator? Seems a likely culprit....

I would think there is a problem with the speakers. 9 DB down in the highs? If the LRS sounds good on the same equipment in the same room, something wrong with the 1.7s.

Check the tweeter fuses?

Getting good measurements of large dipole loudspeakers is not trivial.

By way of example, John Atkinson uses a fairly sophisticated quasi-anechoic measurement technique and you can see his frequency response measurement of the Magnepan LSR on this page, Figure 2:

https://www.stereophile.com/content/magnepan-lrs-loudspeaker-measurements

Compare that with the frequency response Amir Majidmehr of Audio Science Review recorded using a state-of-the-art, hundred-thousand dollar computer-controlled Klippel measurement system, second graph in the first post on this page:

https://www.audiosciencereview.com/forum/index.php?threads/magnepan-lrs-speaker-review.16068/

There is so little resemblance between those two curves that you’d never suspect they were the same loudspeaker.

And imo conspicuous by its absence is the "in room" curve that John Atkinson normally runs, perhaps because he was unable to get good data using his normal in-room-curve measurement technique.

My point being, it is extremely unlikely that casual non-gated in-room measurements made with a spectrum analyzer are "accurate" when there is major inconsistency between far more sophisticated, industry-standard measurement techniques. This is a situation where I would say, trust your ears far more than you trust your measurements.

Duke