My general view is that sticking a tube into a DAC is a gimmick designed to sell product to those who automatically assume tubes=good and solid state=bad. As a serious tubehead, I still think that solid state has some very good points and is capable of excellent sound if designed well.
The DAC I chose is a clone of Nelson Pass' D1. All chips, nothing analog in there.
And I don't have a problem with that.
If tubes offered some kind of advantage or benefit (aside from the OMGTUBEZ! aspect) in a DAC, then I'd think about it. But I don't see any serious engineering *reason* to put tubes into a digital device. All I see are marketing reasons. That's not to say you can't get decent sound from a DAC with tubes, but you have to realize that they're in there more for marketing than for a technical reason.