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

I had a similar problem with my MMG's last year. I thought the tweeters were blown, however, I took a shot and tried this: I removed the binding post plate and found that the wires from the crossover to the plate were slightly loose. I tightened them up and they're back to normal. I don't know how this happened, perhaps through shipping. Either way, it might be worth looking into. Best of luck.

Jon

Sounds to me like you set everything up right.  Those stock steel jumpers are junk.  Pass Labs have plenty of current to drive those ribbons.  Anticables work well with Maggies but maybe you just need more break in time.  You may try tilting forward a couple inches to see if that helps because what you are describing doesn't make sense.  I owned 1.7i's and used Anticables and their jumpers with high current amps and the one thing that was never lacking was upper ranges.  And don't be  influenced by measuring devices.  The two best ones you have are the ones on either side of your head.

The crossover in the 1.7i is pure junk. Replace the capacitors and the inductor, ditch the stock  wiring. Lose the fuse
And you  will have dynamic range coming out of those speakers that you  would not believe. 
I am saying this, because I have a pair myself, and did all the upgrades. 

Absolutely @yuviarora, the binding posts as well (Cardas posts will fit right in the stock holes). That whole plate is filled with ferrous parts! Have you watched the GR Research YouTube video in which Danny Richie measures the 1.7 and looks into it's x/o? Well worth your time. A YouTube search for "GR Research" will bring up all Danny's videos.

@bdp24 I haven’t watched that video, but I will. The post was the 1st thing I chucked, now my crossover is soldered onto my cables directly.
I have Mundorf Evo Supreme oils for the mids, Mundorf Supreme Silver oil for the Tweeter, Jantzen wax 12 gauge Coil inductor for the Bass, Neotech 14 gauge Solid OCC Copper for the internal wiring.... The speakers sound incredible, Jazz is just to die for.
One of the coolest surprises was Electronic music, which previously sounded like monkeys beating pots and pans on the speakers, is now one of the most detailed, crisp 3 dimensional sound I have heard on any speakers.
My friends call the Maggies "The Spaceship". EDM sounds like a mushroom trip, no distortion whatsoever.
Fantastic speakers, but the crossover upgrade is an absolute must in my opinion.