For the amplifier, I just tried the pair of 1266 phi cc + XiAudio’s Formula S for a straight week. Before that, I heard the combination of 1266 phi + Wa5. I have to say I love the XiAudio combination. It’s clear and precise. Superb bass. Great soundstage and chords are always very balanced. It’s a China brand though, but I understand that Abyss is using it as some kind of official set for their exhibits. Not sure the accessibility of Formula S outside of China, it’s extraordinary.
Very happy with the Abyss Phi / XI Audio combo (Formula S amp + Powerman PSU) here as well. JPS Labs / Abyss dealers worldwide are selling the Eleven Audio gear, I believe, so accessibility should be relatively easy.
I don't use an amp with my M-DAVE. I felt the same way you did BTW. In particular, I found the midrange to be too distant and clinical. It simply didn't engage me. Instead of selling or getting an external amp, I decided to try a different HP cable. I bought a Lazuli Reference and that improved things but not enough.
I then bought the JPS Superconductor HP cable and it literally transformed the Abyss. Just an incredible cable! It's bloody expensive but it negated the need to buy an amp and importantly, avoid messing with DAVE's transparency by putting an amp into the chain.
Maybe an external amp would help beyond the midrange problem I solved, I am not sure, but I can say that the Superconductor / Abyss combo is magical, particularly for vocals...
DAVE drives well the Abyss Phi in my opinion, but when I added the amp I found large scale orchestral pieces, organ, big bands etc. were just more satisfying, with plenty of air / lack of compression. Layering and readability of the music was kept very well even on fortissimos and very crowded musical passages. Also, extreme dynamics piano pieces are effortlessly reproduced.
I was struggling to get a realistic SPL with very low level classical recordings with DAVE alone (and M Scaler / Blu Mk2 makes this slightly worse due to "stealing" 3dB of additional headroom), where with the Formula S in high gain position I have abundant power reserves.
For some music types and or tracks, I still like the M Scaler / DAVE direct more, where the detail retrieval, transparency, 3D sound staging of the Chord source is delivered at the extreme, but most of the time I use the Formula S.
As for vocals, I was thinking that the same as @spotforscott when I was using DAVE alone, but the addition of the M Scaler ha provided a significant improvement to vocals naturalness, warmth.
That said, I am looking for a JPS Superconductor (see my classified here) to complement my DHC Prion4. The Prion4 is very detailed, liquid, transparent, fast and open sounding, and I like it very much with classical (I preferred it to the Lazuli Ref. just because of its extreme transparency), whereas based on the reports the Superconductor provides a richer, darker midrange that I would like to try for intimate recordings such as vocals, jazz etc.