You cannot come up with two amps more different, opposite ends of the spectrum. I own Audio Research Reference 160s and had 160m monoblocks for over a year and a half. I have spent a lot of time listening to the Luxman.
For me, there is just no comparison. The Luxman is very solid state sounding, neutral, flat, not musical, with the ability to handle really low impedance loads. The Audio Research is a masterpiece in musical presentation. Fantastic rhythm and pace, midrange bloom, incredible nuanced bass.
If you are looking for a very analytical amp, capable of lots of detail, emphasizing the venue and mastering techniques and slap you in the face with a single wave of bass, then the Luxman is your ticket. If you are interested in music, then the Audio Research.