My current system is a Luxman L590-AXII driving DeVore Gibbon Super Nines. My source is Lumin U1-Mini (w/Sboosterj and Denafrips Venus II. Also a Rega P3. Speaker and interconnect cables are circa late 90s Cardis Cross There is a lot that is right about the sound of my set up, but I feel it’s lacking fullness in the midrange.
It’s the speakers. I find the Luxman L-590AXII to be very close to neutral with low coloration. The thin and lean sound you are getting is likely from the Devore speakers. Get the speaker-amp match right the L-590AXII is highly capable. The Luxman shows a level of clarity that may be missing with other amps such as Pass Labs which focus on other aspects of sound reproduction such as throwing a large expansive sound. The focus of the Luxman is more toward micro detail and nuance with a more delicate touch.