Amps under $5k that are resolving at low volumes?

I would concur that the Maggies may be the main factor with the low level resolution.
Having owned 3 different pair, low level detail is not what they are about.
If you are after low level resolution I would recommend full range electrostatics or horns.

Best set-up I ever owned for low volume listening was a Pathos Twin Towers into Vienna Acoustics Mozart's ... a close second was a Cary 300SEI into ProAc 1SC's

Merrill Audio Thor monoblocks

Actually I have no problems with the 1.7's sounding shrill... every shrillness concern I had with them resolved to be caused by other components. But full disclaimer also... I replaced many of the "no name" original crossover capacitors in my 1.7's with Clarity CAP ESA's and Mundorf Supremes

The original reviewer criticisms of the PL Premium integrated were 2 fold (1) weak lower octave (2) a dissatisfaction with ability to resolve at lower volume levels. KT-150's have addressed the bass short comings but I fully agree that you can't get good enjoyment with the amp at less than "robust" volume... my old Hafler did better at low volumes.

"03-16-15: Davide256
Actually I have no problems with the 1.7's sounding shrill... every shrillness concern I had with them resolved to be caused by other components."

I've heard that one before, lol. In all seriousness, though, even to play at moderate volumes, your Prima Luna is probably working pretty hard. Generally speaking, tube amps are a bit more forgiving when pushed hard compared to SS. So while you may feel the need to turn the volume up to get everything sounding right, its possible that the amp is straining and you just don't realize it, tubes will sound different under a heavy load. I didn't really care for my 1.7's, but I didn't have any problems with them at low volumes. Do you have anyone that can lend you some components to do some testing with?