Two more questions:
1. How does it compare to the GSX MK2? I'm really looking for a TOTL solid state amp and after owning a balanced Dynahi, I was really disappointed in the GSX MK2.
It would be interesting to line them up together. I suspect the GSX2 may extract more plankton by a small bit; but most of my impressions with RT have been with Loki or Wyrd/Modi, which aren't the most resolving DACs on the planet. The RT could probably be categorized as having a dark tonality - probably similar to your 2A3mk4 or 300B BAs. The GSX2 in comparison is lean sounding with a strong etch, and really not all the controlled, actually kinda of raw - without poise in the treble, especially at the higher gains. The RT has better precision and control of the driver - although I'm pretty sure it's output Z isn't super low. (I'll measure this before I send up to you.)
The GSX2 sounds flatter at medium and low gains. Yes, the gain setting changes the sound. Higher gains result in a more lively sound, but more difficult treble. Low gains have better treble poise, but overall sound is flat and dead.
I think it depends upon what kind of sound you want and what DAC and headphones you pair it to. The amps are on opposite ends on the spectrum in terms of tonality. I using unmodded HD800s from RT from Wyrd/Modi.
