A DAC is an analog device. What do you think the "A" stands for. It is also a digital device, but the digital part is a go/nogo thing and not likely to affect sound quality. The analog output of a DAC chip is fast and accurate, but generally needs a buffering circuit to provide a low impedance signal for output to other parts of the audio system. I think that the question relates to the quality of this follow-on circuitry. In early CD players this is where manufacturers chose to cut corners, and many early CD players were significantly improved by replacement of this circuitry. This is still common practice by MOD shops, even going so far as to install tube stages. Few, if any, MODs involve new DAC chips.