Most likely what you like about the X350 is the slap you get because of the really fast bass… the slam. You’re not going to get that with tubes. Also, that is not real. I spent over ten years going to hundreds of concerts and that bass slap doesn’t happen in the real world. I used to crave it as well… then realized that when you switch to a Conrad Johnson, Audio Research, or other high quality tube amp you get much more. You get highly detailed natural sounding bass and fully fleshed out midrange smoothly transitioning to bass. The very fast powerful solid state generated bass tends to be monolithic and accentuated by a leaner than real lower midrange/ upper bass. There are great detail
Terrific observation!
I do believe that the higher damping factor (DF) is appealing and its effect on bass is desirable for many. In my experience it adds a “tightness “ to bass frequencies that I just do not hear when listening to actual live acoustic lower range instruments. So I clearly understand your point. Nonetheless, the DF tightening is sought after.
Charles