Polygonhell
100+ Head-Fier
On a serious note I don´t think tubes have any high fidelity. First it makes limitations to the sound with distortion and lower resolution, and then the soundstage lacks behind.
Been said, tube amps aren't about the distortion, except at the entry level.
Tubes are a more linear voltage amplification device than transistors are.
I have a pair of Tube mono blocks here most wouldn't know had tubes in them, and you can get everything from fast, "sterile", to relaxed warm from almost any tube with the right circuit.
Soundstage is also better on most tube amps.
Not even going to get into the magic that is a DHT.
Where tube amps lost out to SS was in the 90's when they changed the efficiency rating on speakers from dB/W to dB/2.83v, which was done to allow smaller speakers to have better bass without seeming extremely inefficient because they would drop impedances to < 2 Ohms at some frequencies. Tube amps aren't really designed for inefficient a wildly varying load and it gets expensive to build a tube amp to drive speakers like that.
None of this is an issue with a Planar headphone like the Susvara, assuming the amp has enough grunt, they can be VERY good, it's just unusual for tube headphone amps to have enough grunt.