Thanks for the comment, Anand.
It is more of a slow simmer

I have a couple of the Salas Ultra BIB V1.3 boards that have been sitting on my bench for far too long.
Hopefully I can populate them and install them in this DAC before the new year.
OzarkTom,
A lot will depend on what power supply is used for the opamps. With the Salas regulators, the difference between opamps show up rather easily.
The Sparkos Labs are very good sounding. Quite a bit better than most non discrete opamps.
In this circuit, I do prefer the Burson.