If the DAC isn't (sufficiently) transparent then putting a valve (tube)
in series with it cannot make the combination transparent. Yet
sometimes I see the T word used to describe
"better" in this context.

Isn't a DAC by definition something with an analogue output stage? So
something must be on the end of it, whether ss circuit,
transformer,capacitor or tube stage. The advantage of a tube stage is
that the output with DC on it can be fed directly into the grid of the
tube, and the DC included in the biasing. You can't talk about a DAC as
if there's "nothing" on the end of it.