Is there any reason you are looking for NOS?? The 'no moving parts' aspect of a DAC would limit the number of things that are likely to go wrong (generally electrolytic capacitors, which can be replaced), and the lifespan should be quite long. I have a DAC with the UA 20400, and while not discrete resistor, I think it was hand trimmed resistors. Really delivers a wonderful sound, and available in DACs from several vendors - Stax, VTL, and Sonic Frontiers. Directed at Redbook, and likely within your budget. Sometimes older is better .....
