Here are my guesses:
1 is B orA and is the iphone or bluetooth receiver
2 is C and is the SMSL stack
3 is B or A and is the iphone or bluetooth receiver
4 is D and is the Topping
So, I think I got the numbers and letters paired up right, though 1 and 3 sound identical, so realistically, it's a crapshoot, I could just make a straight guess, but why bother. The levels on 2 and 4 are different than the other two, so, it made it a bit easier to match them.
I found that I heard 4 get louder and softer than the other 3. 4 also seemed to reproduce a better timbre when it came to the cymbals, which was the detail I was most closely paying attention to. 1 and 3's cymbals sounded like impacts, 2 and 4 carried the sound through a bit more, to my ear. (There's a particular cymbal crash 39 seconds in that decays for about a quarter second longer on #4 than any of the others) My subjective opinion is that 4 was superior, and to that end, I'm giving the one that I believe had a perceivably better sound to the DAC/amp that measured better, objectively. Number 2 was louder than the others, so it was harder to tell if I enjoyed it more than 1 and 3 because it was louder or if it was actually better, but I ultimately thought 4 was better anyway. 1 and 3 are, as far as I can tell, identical.
I'm extremely interested in knowing if I actually like, for instance, the iphone's DAC, better than my own Topping! That would certainly be eye opening! It's possible that the Topping and SMSL offerings are 1 and 3, since, deductively, they are both ESS DACs while the other two have Cirrus and AK DAC chips and it's possible I simply prefer the sound of one of the others.
Either way, thanks for the distraction!
I listened to everything using VLC player through USB to a Topping DX7Pro into a ZMF Auteur via balanced 4 pin out and also through the Topping, into an Emotiva A100 to an ifi iesl to a pair of Stax 007mk2. I only heard differences in the files with the Stax setup.