Well, since I have the Eros, BeePre and Stereomour II, I thought I might as well have a listen to a full Bottlehead pre plus amp system. I simply fed the output of the BeePre to the Stereomour with the volume pot on the Stereomour wide open, controlling volume with the BeePre.
The combo definitely produced more volume and impact than the Steromour by itself. It's a really nice combination, with a really deep, broad soundstage and tons of detail in the music. I'd say there was a bit less control than with my FirstWatt, but a bigger sound. I didn't spend much time playing with optimizing the two volume controls as I was able to get to 1/2 way up on the BeePre volume at solid listening levels. Some of this may be speaker dependent, as the Zu is pretty efficient, but my feeling is that it likes a little more power with full scale music. I was listening to Ryan Adam's self titled solo album which varies between acoustic and full band.
I'd endorse the combination, with some thought to speaker matching for the power output of the 2A3s.
James