Interesting that you find Pass to be 'lean'. From all my reading of Pass and their lower end heft, I would have thought it provides a bigger, fuller body to music; which is to my liking.
Yea, I don't personally get the description or hear Pass to be 'lean', at all...; as someone who currently owns the XA30.8, have owned the X250.8, Bryston 4B3, Benchmark AHB2, and Modwright KWA 100SE, I would personally place the Pass on the slower rounded side compared to all of the others I mentioned. To me the Pass adds depth and meat to the sound, and if that is what you like, like I seem to, it sounds so life-like and easy to listen to. The most recent additions to my system to compare against the Pass amps were the AHB2 and 4B3 and I felt they both offer a more resolving and leaner presentation (still smooth though); you hear more of the recording, but I thought they also lost some of the 3d like humans are playing in your room quality I hear from the Pass.
The only recent Luxman I've heard was the C-900/M-900 combo driving the speakers I ended up purchasing and now own, at a local dealer. I thought they sounded great, lots of detail and very smooth; I wouldn't call either of the two Pass amps I've owned 'lean' compared to the Luxman separates.
Definitely try to listen for yourself...; worse case either a Luxman or Pass shouldn't be hard to re-sell if you grab one and end up not being happy with the purchase.