I am sure poly will explain more but here is my very basic stab at it. Driver tubes in high fi normally put the audio signal to a spot where it can be used by the output tubes. Usually “driving” the signal to a spot where the outputs are more linear. This looks to be using a transformer to do that job.
I wonder if it will help with the sound floor issue i had with sensitive headphones.
It’s basically a transformer based pre stage, so the source is driving the power tubes directly through the transformer .
The issue with that is going to be the effect on the input impedance, the impedance scales with the square of the windings, so assuming it’s say a 20:1 gain (it would probably have to be more than that) the input impedance is dropped by 400, so a 1MegaOhm input impedance (might be higher than that, I’d have to do math) turns into a 2500 Ohm impedance as far as the source is concerned.
That won’t be an issue for most SS DAC’s, but it might be an issue for sensitive sources, it’s hard to guess without doing the math or simulating it.
Just the requiring 4 12AX7’s and 4 EL84’s would put me off.
I don’t retube my power amps until I have to, because the thought of replacing 16 tubes makes my wallet cry, but at least that puts out 130W.
8 tubes for 3W just seems unnecessary.
FWIW I think the only Focal that works well with tube amps is the Utopia, the Elex and Clear tended to demonstrate a loss of bass control and much less coherent imaging on the amps I tried with them.
Having said that I’m not sure I had anything particularly high end tube amp wise when I had those headphones.