I haven't heard the Doshi v3.0 preamp but I own v2.1 and it was the direct replacement of my previous preamp, the Audio Research Reference 3. For what it's worth, below are some of the sonic qualities (from what I remember) I noticed during my the Doshi v2.1 vs ARC 3 comparison. Both had good sounding tubes that were broken in (ARC tubes were from the dealer). I also brought my friend's ARC REF3 into my system to be sure mine wasn't in need to tuning.
* Doshi v2.1 is very fast. The ARC REF3 is sluggish in comparison.
* Doshi v2.1 is very clear. Details on recordings are revealed better than what I heard with the ARC REF3.
* Doshi v2.1 has fantastic timbre/harmonic qualities. It's a hybrid design but it doesn't sound analytical and has the right amount of tube sound. The REF3 sounds murky or "tubey" in comparison.
* Doshi v2.1 has a better sound stage, holographic and instruments/vocals placed well in the image.
The Doshi v2.1 was a big step up for me. I've also compared it to another high-end preamp, within my system, that costs much more and I believe that the Doshi preamp is a great value.