For the HD800S I owned, I also used a tube amp made by a local techinician. With the vintage, unmatched 6SN7 tubes the amp came with, the 800S still sounded a bit lean, but better than with a solid state amp. I swapped the 6SN7 tubes with a matched pair of PSVANE CV-181 Mk II, and it was a world of difference. At the same gain level, they sounded louder, more powerful, but could get a little overwhelming after a while. Sadly, the glass on those PSVANE tubes is very thin and, thus, fragile, they felt more like eggshells, I broke one of the tubes when I was stowing the amp inside a drawer. I replaced them with a matched pair of vintage NOS Sylvania 6SN7GT tubes, and while not as good as the CV-181, they were definitely better than the ones that the amp came with.
Sold the amp and the remaining PSVANE tube to a guy that lived in the middle of nowhere, but happened to own amps made by the same technician. Such a small world we live in.
With the L700 Mk 2, I tried the blutak mod, both with full and partial seal. With full seal they farted all the time and, honestly, they sounded rather plasticky without EQ. With partial seal they don't fart and they sound a little better IMO, specially with EQ. I would love to try one of those 3D printed spacers because the tip of my ears do touch the protective mesh.
For DAC, I owned a DENAFRIPS ARES II, which I sold about a year ago because I wasn't really that impressed with its performance and I needed the money for other projects. I kinda regret it now, specially after reading from other ARES II owners that the last FW updates improved the sound quality quite a bit.
I dunno if I should believe those stories.