The only thing I can say is that lately we do one thing only : looking (listening) for wrong / unnatural playback of voices and instruments and all.
Currently we are *very* satisfied. Note that this is XXHighend/Vista/Engine#1/96K, and the Orphean/BD15/MKII. The latter is probably the most important. As a bonus the BDCrazyA is used, adding spooky air to it all, and making you see the shivering of cymbals.
We are now *really* in the stadium of comparing music playback to the real voices and instruments, and therefore we are close to comparing by absolute means ! Close or just there.
Currently it is very hard to tell what can be a next step. Oh, I know one : Vista/Engine#3, which currently makes too much of all (mainly dynamics), of which I am sure that this is "limited" by means we did not find yet.
We'll see !