Tube rolling newbie- how to choose NOS tubes

+1 for Brent Jesse his advice is top notch and his return policy is more than fair. Basically you pay for shipping and get to try something else within 30 days no risk.

But definitely let the stock tubes break in if the DAC is new and get used to them as others have said.

Many of the reissues are mediocre, some are good for the specific application (JJ comes to mind).  

You will learn a lot and get pricing from his web site here: audiotubes.com/12au7.htm

Emailing him is best, explain what you have and what you are looking for. Don't get stuck on Mullards though (nothing against them, I have a pair in my DAC from Brent that I love but they were $450 a pair) but there are other great NOS options that might be obtained for less.

Not sure what the rest of your system is but there is a point of diminishing return to consider.

complete waste of time and money to buy nos or other tubes without significant run in time for your new component…. burn in, listen critically, discern where you want to go

I disagree with this. Many manufacturers of tube-based gear ship their products with the best sounding, current production tubes that are readily available and don't increase cost of materials too much. Their expectation is that you will roll tubes - pretty obvious, why else would you buy a tube DAC.

All you need to do is leave your DAC on for a few days, identify what you don't like or want more of (in my case it was a high-frequency harshness/sibilance), and try out some NOS tubes. 

+1 @lowrider57 I got my most recent tubes from Brent in less than a week, and that was only because he is really busy.