I don't necessarily agree with some of the statements here. If you address clocking, jitter, etc. then a good dac is a good dac. Either it does what it's supposed to do (correctly convert a digital stream to analog) or it doesn't.
The systems that go back and forth to make sure that it got the correct data before proceeding, multiple laser pick ups, error correction, jitter, all kinds of things. These all add costs to designs and systems.
i initially was speaking about transports only, then added a few units that have pretty darn good internal DACS.
Now back in the day, these were near top units both in performance and costs. move forward to today, these "used" units for the money are pretty hard to beat. And that was the point.
You take a top of the line DAC today and get a top of the line Transport both today and older transport unit and compare the two into the same DAC. Jaw dropping differences? no. A solidly built transport with good pick up mechanism is just that.
I've also compared top of the line DACS of today with CD players and DACS of the past and guess what? differences? yes. Jaw dropping, not in many cases. Especially DAC vs DAC. Discrete analog output stages and very well designed and built power supplies matter.
but, this is just me. Don't get me wrong, there are technological advances. but if budget is an issue, I would invest in a nice DAC and get a used but very nice Transport. Especially if you could synch the internal clocks.
enjoy