It looks like the HiFiBerry hardware volume control fix is in, at least on the DAC+?
(meaning it is working after the board is enabled in config.txt with no further tweaks)
If so, that is a big Thank You Frank!
Looking at the upper limit of the corresponding "Digital" control in amixer, it seems 100% in the Rune UI now corresponds to 0db, so the numbers on the screen actually make sense, give or take 0.5 db rounding error.
Using amixer sget and amixer sset commands from the command line now works as expected, and I can tear up the four pages of cheat sheets I was using for testing...