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

A cursory glance shows the amp has what - 8, 4, 2 Ohm outputs. If you're on 8 Ohm, try the others. 

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?