... was wondering if a Beepree2 could up the quality of the sound. ...
Leaving aside the fact that you don't need additional gain, my guess is that the BeePre would have a significant and, depending on your listening preferences, potentially positive effect on the sound. I haven't heard the Evo 100, but I assume it's push-pull, in which case I would expect that either (a) it is 3rd harmonic dominant with 2nd harmonic being really low, or else (b) uses feedback to reduce all harmonic distortion. In either case, I would expect adding the harmonic profile of a SET preamp like the BeePre would make a noticeable difference.
I for one love the sound signature of my Beepre 1 (I have yet to build my Beepre 2), and have experimented with replacing it with a high quality transformer-based attenuator -- which (leaving aside issues of cable and miller capacitance) was effectively like turning my Kaiju into an integrated amp. I preferred the BeePre. And I also prefer the Beepre in front of both my Stereomour II's, even though they're integrated and don't need a preamp.
Just my 2 cents.
cheers, Derek