Are "vintage" DAC's worthwhile, or is this a tech that does not age well

@antigrunge2  yes but if you have some sort of USB to SPDIF converter between the computer and DAC then it would take care of the jitter. Once that's done, it could go to any DAC chip. Unless I read your post incorrectly.

It was noticeable improvement in SQ streaming Tidal when I switch to Dragonfly Cobalt from Dragonfly Black in my mobile setup.... so DACs sounds differently to me. 

I have been listening to Theta Casablanca III then IVa ... both with extreme DACS.  I have had recording personnel listen to them as well.  They agree that there is simply no better DAC out there.  New "digital dacs" are difficult to do right.  Now that the IVa has their calibration done in the Netherlands...sound is absolutely perfect. Thetas are built like a tank and like a computer at the same time.  If I have difficulty, I send the unit back to Theta, they replace a board and I am back in business.   Their extreme dacs are the best I have ever heard.   I don't like sending power over wire so I use active speakers...ATC to be exact! 

@curlyhifi. Those Krell SPB 32x, Studio and Ref.64 dacs were some outstanding units!  Thanks for the audio flash back...been a long time since I had them but man did they leave an aural impression.  Oh boy, guess this guy is going to start hunting one down to play with again.

The old vintage dacs will sound absolutely wonderful but you will not be able to hook them up to all the new forms of digital equipment or computers but if you want to hear the best digital sound a vintage converter will stomp all over the new stuff no contest.