I know nothing of the workings of them, only that you supposedly get a rich analogue sound from them. I'd love to try one some day.
Then I am very suspicious of all the hype surrounding valves, the reason technology moved away from them was they are big, costly and inefficient. The sound might be pleasing but is it more accurate? The argument sounds very much like the £5000 per metre zero oxygen copper cable is better that £5 per metre copper cable. Then in most cases people are pumping a digital signal through valves.
I'm not arguing that you shouldn't use one with a genuine1960s guitar, they were made for each other and give a distinctive sound.
I have no experience of vintage tube amps but I do have 2 modern headphone tube amp’s, one on my HTPC (which is the main one I use for music listening) and a cheaper one of my gaming PC.
I do enjoy the sound tubes give to music, the set I'm using on my HTPC at the moment are new old stock USSR tubes made in the 70/80’s for the nuclear program
https://www.ebay.co.uk/itm/LITTLE-DOT-MK1-MKII-MK-III-HEADPHONE-AMP-ULTIMATE-VALVE-TUBE-UPGRADE-UK-STOCK/252130624590?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649Serious nobody pumps a digital signal through a tube amp it would be gibberish
(or speakers/headphones for that matter) that is what a Dac or sound card does turns a digital signal to analogue. As for accuracy (outside of the recording studio) for 99% of people who listen to music a more soft sound is often better than 100% accuracy. I have quite a large collection of high bitrate 24 and 32 bit audio and some gets quite fatiguing to listen to after as little as 10 minutes at my normal listening volume. The tubes I'm currently using opens up the soundstage, tightens up the bass (makes it more defined) and tone down sibilance and makes the sound a lot more pleasing on the ear.