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

I have a pair of 1.7is. I recommend until you are very familiar with the Maggies and sort this issue out, that you run them only on solid state equipment. I have not looked up the specs on those Pass Labs monoblocks. But I would use those and the Pass Labs solid state preamp. I would put back in the stock steel plate jumper for now. Also check the fuses to make sure they aren’t blown. Make sure all your cable connections are good ones. Play music that is well recorded. Examples would be Steely Dan Aja and Goucho. If there still is a problem call Magnepan. Normally the highs aren’t as big an issue as the lack of bass impact. When yiu get this sorted there are other modifications that would make a difference. 

As most things tech, usually the fixes are simple. When they aren’t simple then it’s a big problem. Just put in the stock jumper and hook up your high watt ss system. Angle the panels so the tweeters are pointed at your listening position. Assuming your fuses are ok, what do you hear? Highs should not be an issue on Maggies. How many watts output are your monoblocks? Maggies like high power. I am using a pair of Bryston 28B3 monoblocks for instance. Schiit Vidars are not enough. I used to run a pair of Vidars and one went into thermal protection. 

@yuviarora did you install the GR-Research Maggie upgrade or are the parts you mentioned above something you selected yourself, or was your upgrade obtained from someplace other than GR-Research and if so, where? I have a pair of 1.7i. Thanks!

@eatapc Hi. I am a former Maggie 1.7i owner. This is what I recommend:

1. Magnepans NEED subwoofers. They do. They are ribbon speakers with no air movement and no percussion. There is no slam. They need subwoofers. I added a pair of REL T/9i subs to my 1.7i and it revolutionized the sound. 
2. I agree the binding posts, fuse and jumper are steel plate garbage. I replaced the steel plate jumper and cheap fuse with Mike Powell’s silver upgrade. It’s a sliver humper and a silver tube replacing the fuse. Those changes greatly improved the top end. I am sure if you are handy enough and can replace the crossover and binding posts, more benefits will accrue. 
3. These Maggies need powerful solid state amps for regular driving, but also for headroom and dynamics. Schiit Vidars are insufficient. Amps like the Brystons and Pass Labs are good. 
I hope this was helpful. 

@bdp24 your point is well taken. The point I was trying to get across is that Maggies do not move air. They don’t have traditional drivers they move air. Hence, no persuasiveness in the sound. 
 

@charliech No high pass filter used. RELs were connected to amps with high level REL cables made by Kimber and later Analysis Plus to amp binding posts. Crossover was tuned to my Maggies and the room. It’s been a while since I had the Maggies in my system. But they were crossed likely at around 80-100Hz. 
 

I would also recommend getting the Mike Powell silver Ag Maggies upgrade and putting the 1.7i pairs on better stands. 

@bdp24 Yes. I meant “pecussiveness”. Autocorrect messing me up again.

My experience with Magnepans are my former 1.7i and the AXPONA tests of the LRS and the LRS+. I added a pair of REL T/9i subs to my Maggies and it made a world of difference. Not hard to dial in. But I think the addition of the subs and what kind of subs could be room dependent. I have thought about getting a pair of LRS+ just for kicks. I haven’t pulled the trigger on that yet though. Going to AXPONA at the end of the week. Maybe something will happen there.