thanks Rashiki and NB.
Rashiki... jitter... I thought that only affected CDPlayers and was due to the spin of the cd reader. I had assumed that jitter would be eliminated in any digital memory storage, like a harddrive. Is that a misunderstaning on my part? (edit: nevermind. I did read up on jitter. Big misconception on my part. Thanks!)
NB... You said it's important to separate the dac from the computer's powersupply with a digital cable be it optical or coax. That's interesting. I've seen alot of rather expensive solutions that connected a DAC right through the USB (a version of the benchmark dac1 for example) these must incorporate the pulse transformers you mention.
I'm doing this from scratch, and it will be a slow process. At the moment I only have a CDP, pre- and amp, and speakers. And a laptop. The next step will be a NAS or external HD and some means of communicating from computer to the stereo. I was considering the Behringer u-control uca 202 which is a smal usb device with a small dac (48 khz 16bit) and an optical out as a cheap middle step before I moved on to purchase a DAC separate. On the other hand, the SB3 isn't too expensive for me and may be the more flexible route because it does let me use the wifi, which I do use for my computers, as an intermediate step.
Just trying to chart the best upgrade path that will leave me with the highest quality final options. In the end, the sb's powersupply might be a limitation? I've read in a number of places the the sb in the final analysis is not a hifi solution, perhaps because of the 48 khz limit you mentioned. I've seen some well reviewed mods, the most significant changes were the addition of much bigger powersupplies. These were getting good reviews.
Thanks again!