Why are digital streaming equipment manufacturers refusing to answer me?

Again, you obviously don’t understand ABX testing which is NOT about absolute identification, i.e. picking out the 98 Bordeaux from the 96 and the 99, it’s about having 3 bottles, two 98, and one 96 and being able to tell the two 98 are the same. If you can’t tell a 96 and 98 apart then you don’t actually prefer one over the other. ABx increases the statistical reliability of an AB test. ABx testing IS a preference test essentially as it requires no absolute identification.

It's about saying a = x. That is an identification judgment. You don't have to believe me, but the brain is worse at that than at determining preference. 

They have studies with patients who have zero long term memory. Every day they fail an X test by failing to identify people with whom they've interacted with repeatedly.

Nonetheless, they form adaptive preferences for these individuals based on whether those past interactions have been positive or negative.  That is because the area of the brain responsible for preference is different (and more basic & important) than the area responsive for identification.

Your example is an absolute identification test. As noted this is not applicable to the discussion. You seem to be missing the point.  If you have AB and X. And have a definite "preference" for A, then when x=A, that preference should replicate.  You try wine A and B side by side. You claim you prefer A to B.  Now I give you wine X. Do you claim you prefer it to wine B? If so, it must be A right? What if it is actually B?  That means your "preference" was random.

They have studies with patients who have zero long term memory. Every day they fail an X test by failing to identify people with whom they've interacted with repeatedly.

  I suspect if you instructed people to base their identification judgments in an abx solely on preference they'd do significantly better.

Actually what results in better ability is training in the characteristics of differences. The natural tendency is to rely on "preference", which is very fickle.

Nonetheless, they form adaptive preferences for these individuals based on whether those past interactions have been positive or negative.

Which would require learned neural patterns. This is not related to directly to ABx and more related to why blind testing is necessary to ensure the learned neural patterns for looks are removed from sonic decisions. However as applied to ABx, those learned neural patterns should trigger the same for A and for A=x, as opposed to B.  It is also why training improves ABx as you develop additional neural pathways for characteristic detection which is what preference is. 

When people get the X test with audio equipment I suspect many are trying to figure out if the treble, bass, image depth, tonality, etc. match A or B, not asking themselves how much they like the presentation and then seeing if that preference is closer to how they felt when they listened to A or B. Of course we’ll never know if that’s true because unfortunately I don’t run an audio testing laboratory.

And yes, there is learning happening in the memory patients, but the area of the brain that makes explicit identification judgments does not have access to it. I’ll also note that when they fail to recognize a previous acquaintance that new/old judgment is even easier than matching to a particular object as required to succeed in ABx. Despite utter failure of explicit identification, the preference system chugs along just fine, leading to adaptive decision making.

This dissociation is why it is incorrect for you to state that, "if you can’t match A or B to X, then you can’t tell the two apart and you hence have no preference as you don’t as actually prefer either."

Anyway, it’s clear you’re going to continue to believe that matching judgments are the appropriate way to do A B testing. And that’s 100% not how I would do it if I were optimizing people’s decision making. It doesn't matter if you can pick your stereo equipment out of a lineup, it matters whether or not you like it. So be it...