Can't really explain the difference between the V90 and the Vali, or even say which I prefer!
Using the V90 as a DAC/amp, it's like the mids and vocals are a LOT more prominent. Definitely more treble to it. The V90 as a line-out from my Modi 2 Uber feels a little flat in comparison, vocals also sound a bit more recessed and blended into the rest of the music. A bit odd as the M2U is supposed to be a neutral DAC, unless the V90 DAC isn't neutral, maybe explaining the emphasised mids?
Moving between the V90 as a DAC/amp and the Vali is harder to AB with having to change RCA. I'm pretty sure the Vali sounds a lot better paired with the M2U than the V90 paired with the M2U. But the Vali compared to V90? Hard call, I'm not sure I could decide. Listening to the Vali right now, the vocals are certainly emphasised using the M2U, I'm not sure there's a whole lot of difference between the M2U/Vali and V90 as a DAC/amp .... difficult.
V90 has slightly more punch to it all, Vali is more relaxed. I guess both can suit different moods of what you want to hear from music at a particular time.