Congrats on owning a great amp, and joining the Moth brotherhood. I am the proud owner of one of the tiny handful of Moth Si2a3H amps that Craig created somewhat in the interim between Moth closing down and Eddie Current becoming fully operational.
Mine was the protype for the others and is a fabulous amp. Roughly a year ago, Elrod-Tom, Jude, Tuberoller, and a few others got to audition it at the special, "Snowstorm In April" meet here in Detroit. At that time, it wasnt fully tweaked with optimal tubes. It's significantly better sounding these days and has awed everyone who has heard it since.
While the quality of the 2a3 tubes are, as previously discussed, very important, dont neglect the others. I am running some superb Mullards in every other socket, and the sound is remarkably improved, and different.
I've been considering picking up some Emission Labs 2a3's, and Craig most highly recommended the AVVT Meshplates, but availability and pricing on those is simply insane. Again, congratulations on owning a wonderful amp.
As a bonus, my Si2a3H drives K1000's beautifully from the headphone output too!