Vintage DACs. Do they hold up over time?

The DAC's you list are very well made. They should continue to work for many years to come.

Hold up? Do you mean quality of sound compared to modern dacs or will they keep working?
Alan

If using them for Redbook cd (pcm) replay, then yes if they have true Multibit d/a converters inside.
As Multibit converters have "Bit Perfect" conversion for PCM (Redbook)
They will give better sound if good ones, than todays Delta Sigma based dacs can.

You can do searches to find if they have Mulitbit dacs or Delta Sigma

Cheers George