Tonal balance will change dramatically with tube choice. I purchased my PA100 used and it came with VAC chinese KT88's and RT driver tubes and the sound was basically big, fat, warm tubey bass, a nice mid, not much air on top, but for the music I listen to most often, 60's jazz it sounded very beguiling but at a disadvantage with rock and classical. I changed the KT88's to Svetlana's and that is the best compromise for me. Nos Sylvania 6189's will give a bit more extension at the extremes with a loss in the mid-upper bass but not in bass impact. This would probably be a better driver tube for rock and classical. With my setup as described, I find the sound to be warm, detailed without being in your face, bass that is full with enough impact to shake the house on something like "Enya- The Long Ships". The top end lets you hear all the cymbals and horns without making your ears bleed. I dislike the pinched over-controlled bass that solid state presents and the harsh harmonics of a piano, so for me I am happy with my VAC and Nautilus combo.
