Maggie 1.7i's lack detail. Ideas?

37 yrs ago there were MG3s, with the first "true ribbon" tweeter Magnepan made.  I owned a pair, and their palpable realism and detail far exceed the Quasi-ribbons of the 1.7is of today.  So that is a big part of it, but also, using a Marantz NR-1200 as your preamp cannot be helping.  #s 1-3 must also be considered as likely culprits.

If you want to maximize your existing setup, the first thing I'd try is to get a legit preamp and a DAC (or one with an onboard DAC) and switch to a true CD player as transport.  Pro-Ject makes a Pre Box S2 Digital and CD Box S2T you can try for under $1500.00.

Also, 1.7is only disperse full range treble if your ears are aligned with the middle third of the panel...if you are too close, too high or too low, they drop off drastically, as I'm sure you've noticed.  Make sure you are in the sweet zone!

Buy a cheap secondhand Marantz sacd Cd player and a smsl dac.

I had the 3 and the 20 and now 1.7i the ribbon is also not the problem.

For example i drive mine mg20 with 4 cello performances the suite and a FM accoustic cross over with a jadis Cd player. That's the best sounds i ever hear. That was in the year 1993 till now they are writing about it. The 3 i drive with the cello duet and the encore and also fantastic i never used any sub. A magnepan needs power and a decent amp. 

Audiolab CDT6000 Transport and the Musical Fidelity V-90 DAC is a nice combo. You'll spend about $500 for transport (Audio Advisory price for new) You can buy a very good digital cable for less than $250. Audio Art, Straightwire, Acoustic Zen. So many to choose from. I won't name the other 100+ of them. I just own at least the 3 mentioned. Used usually comes with burn in time served, also. :) 

Pre+ Amp combo is a definite. Adcom 555 puts out 320/4 0hm load.You can buy a good 555 for $350 to $500. I have 2 555s and will run them in mono once in a while. ( Claim 800+ watts into 4 ohm. I also use them on my Acoustat Spectra 3s in various configurations. (One amp, bi-amp, 2 amps using the internal crossover)

 The 3.7s are just fine with me. I have had the Acoustats since 1988. I think the Maggies will take me down the road until the 6 feet under pair come out.

and the V-90 DAC can be found for under $250