It would be fully balanced compatible. The amplification would be single ended, but the input and output circuits would/could be balanced. Don't put too much emphasis on balanced circuitry, what is important is how well designed and executed the circuit is. A well designed SE circuit which is well implemented can seriously smoke most balanced circuits, and this preamp is one of those circuits.
Here's the thing, Roy is an unbelievably good tube circuit designer. Don is an unbelievably good circuit tweaker. Don takes a good design and tries everything in it. He finds the best sounding wire, the best sounding capacitors, the best sounding resistors for the filament circuit, the best sounding resistors for the audio, etc.
Roy knows most of Don's tricks, and I believe that he charges less, but don't quote me on that. I think lead time is shorter with Roy. I initially had intended to purchase a kit from Roy, but he moved, and as it turned out, Don had a preamp some knucklehead had ordered, so I got him to add what I wanted to it, and it'll be here tomorrow. Otherwise I would have purchased a kit rather than waiting for Don to build one, or have Roy build one for that matter. I would have used some different capacitors for the outputs, and I would have been a little less particular about using resistor X here, and resistor Y there, but I would imagine that I would have had a pretty awesome sounding preamp anyway. They are both true pros, but Don has more experience tweaking a circuit to squeeze the most out of it presumably. I say presumably based upon hearsay as I have not had the opportunity to do a toe to toe sound off between Roy and Don's best efforts, but that is my understanding.
