Maggie 1.7i's lack detail. Ideas?

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

It ain't the speakers. I have Acarian Alon 4's, Audio Research LS-16 pre amp and McCormick DNA amp..Very happy with setup..Before my father passed away, he asked me to get stereo room 2 with $$ he left, so when I listened I would think of him. Covid had hit. I was familiar w/Magnepan and thought they would be a good compliment to the Acarian Alon 4's. Without demo, I bot the Maggies with Parasound A21+ and Prime Luna pre amp. Spent some time setting the speakers and the sound is better than wonderful. My thought is that you need better matching electronics. If cost is a matter (and isnt it always?!!), buy used solid state at half the price. Only other aspect is you bought these "slightly used". Do you have a dealer nearby??

Get rid of the Murantz.  That is your weak link.