In my opinion, the single most important factor is probably making sure that the digital signal is "clocked" as close the the DAC as possible. Many later models of of high end manufacturers now recognize this, and some, like Wadia, recognized the problem years ago which is probably a major reason why their stuff sounds so much better. But most transport/dac combos out there clock the signal at the beginning which means all the jitter resulting from the reading process gets sent along with the signal and are not dealt with in the DAC process.
I have a DVD-A and SACD playback system so I used a Sony SACD player for SACD and a the transport of a Pioneer "elite" unit for the DVD-A coupled with a MSB "gold" dac. I had serious problems with the jitter with that combination so I bought a Monarchy "jitter box" which not only reclocks the digital signal before sending it to the DAC but also upsamples cds to 24/96 kz.
I found a used upper end Denon SACD machine that played back SACD so well that I couldn't tell the difference between the $2000 Sony and the much cheaper Denon. The Denon let me scrap the Pioneer transport so all the units can be plugged together. The Monarchy box which lists for $299 (although they are dumping the units for $199 right now on the Monarchy web site as they are about to release something new to replace it) does such a good job that my DVD-As and upsampled cds sound better through it and the MSB than those processed by the Denon (better bass dynamics and "slam". . In fact, the upsampled cds sound better through this configuration than the upsampled cds through the Sony unit (which won't process DVD-A, the bastards!).
Hope this info is helpful!
