I built the "Crack" kit when it was first released, and still at the initial lower price. The main difference from the "Headwize" is that it originally used a 12AU7A and 6080, I modded it for a 6CG7 which was a simple matter of wiring the driver tube socket filament to pins 4 and 5 (same as with the 6DJ8 / ECC88 / 6922/ 6N1P, etc)
The power transformer isn't critical, just as long as you can get 150 to 160VDC B+. DC filaments are nice, but not absolutely necessary, as the overall amplifier voltage gain is pretty low, a bit less than 30X total.
The 6AS7G / 6080 is a filament current hog, at 2.5A, the 6CG7 is 600 mA, so at least 3.1A is required, play it safe with 4 or 5 A, the filament winding (or separate 6.3VAC tranny) will run less hot. If you rectify and regulate it, then 5A to6A would be best, The 6AS7 / 6080 platecurrent is approx 25 mA per section, the 6CG7 about 4 mA per section..
I use it with Sennheiser HD600 'phones, it sounds
quite nice!
/ed B