I wouldn’t disqualify older DAC's, there are some fine DAC's that were made in the past.
However, you need to ask yourself some questions, such as: do you want DSD\MQA or maybe even Ethernet connection?
If your answer is yes to one of the above then you probably find the answer in newer DAC's
The big difference in DAC sound in the analog output, while you can argue that all DAC'S are doing the same (converting digital information) there are several methods for that which will affect the sounding, but the biggest sound different relay in the analog section which in the end is responsible for the signal that gets out of the DAC – and there, not all are created equal.