Apologies for the long delay in my reply.
Between the BDA-2 and BDA-3, the BDA-2 provides a warmer sound with less separation between notes. The BDA-3 is cleaner, more accurate, and more neutral but as a result drier to the ear. My personal preference would be the BDA-3, however his preference is the BDA-2. I was also expecting some differences in the soundstage, from my experience comparing the BDA-3 to other DACs. However I did not hear that at his place. But his room is more typical of what you'd find in a nicer home, whereas I have a heavily treated dedicated listening area, so that may have played a role.
Between the 4BSST (not Cubed) and 2.5B3 (Cubed), there was a similar sort of difference but the change along the "warmth" dimension was not as large. The 2.5B3 had much better detail retrieval and a more neutral and realistic presentation. I think the key is more realistic. We both preferred the 2.5B3.
In each scenario we used only one of the newer components. So it was either BDA-2 or BDA-3 with the 4BSST, or the BDA-2 with the 4BSST or 2.5B3.
I can't recall off the top of my head which speakers he had. It was a traditional dynamic speaker with a spec'd minimum impedance of 4 ohms, but higher than normal sensitivity, IIRC.
