The Stereomour is optimized for high efficiency speakers, but does not have the noise performance required for headphone use.
Our SEX amp will drive both high efficiency speakers and just about any headphones on the market, and it costs less.
If you're insistent on 2A3's for headphones, you could pair Paramounts with our Submissive passive attenuator. The Paramount has the extra parts/technology built in for substantially improved noise performance over the Stereomour.
-PB