FYI, your view that tube amps take “edge off the famous treble peak/bright sound the HD800S and HD800 often has, even with great solid-state amps” is limited by your experience with solid state amps. I hear no such edge with my CFA3, M^3 ( this one has Staccato discrete opamps) or the head amp directly from Playback Designs Merlot. 800S sounds full, highly dense and weighty, transparent and musical in my systems.
You cannot comprehend the word "often"?