The HD 800 S is one of my main daily drivers. It’s a very good product, but it doesn’t have much bass and can come across as too bright with some setups. Still, the treble is not harsh on a suitable setup.
I run mine on a Decware Zen Taboo Mk IV (my review) tube amp. This amp brings out more bass than I ever thought possible with these headphones. Still, I routinely run it with an equalizer bass boost too. These are my Schitt Lokius knob settings on the Decware, while the two left knobs would be cranked farther with most other amps:
While I don’t disagree much with @gzost, tube amps also add thickness/body through harmonic distortion. Well-behaved tube amps generate a more encompassing and 3D perception of the soundstage, while bad tube amps can smear or rumble or whine and aren’t worth the effort. To my ears, the 800 S sounds substantially thinner on a solid state Class A amp with a bass boost than on tubes.
The 800 S isn’t hard to drive by modern headphone standards, but it’s quite resolving and will pick up on any DAC or amp artifacts your system may generate. If you are hearing bad treble, change your DAC. If are hearing thinness, use EQ and/or try tubes.