If you HAD to purchase a used (over 4 years old) DAC, what would it be?

Anything Ayre would be my choice.

B

There is no doubt I would look for a used Hugo TT2 Dac. The Dave is great too but so is the TT2 and the results are very close to the Dave but at a much more reasonable cost. especially used. There are several on US Audio Mart.

https://www.usaudiomart.com/details/650177141-chord-hugo-tt2-dac-black/

if i had the money doge or lampizator

Mytek Manhattan II

+1 for the T+A DAC 200.   I have one and am delighted with it.   However, I think it’s only 4yrs old; wouldn’t meet the OP’s premise….  Great DAC though.