If the jitter is truly low from the transport, then the problem is likely the DAC. If the DAC does not have a good volume control technology in it, this could be the problem too. Perhaps not that much better than the preamp, just different.
I want you to try modifying the CD disks themselves. This will lower jitter even more. There are several steps you can take:
1) get a really good treatment solution from Jena Labs and treat the disks. Spray it on and then rub with a lint-free cloth outwards. I believe they provide the cloth.
2) try putting the disk under a fluorescent light, up close for 20 seconds before you load it
3) use a degausser, like those used to erase the older cassettes on the top of the disk - this removes charge
4) the best treatment is actually to put a rubbery coating on the top of the disk, avoiding the center where it is chucked
Another thing you can do is rip the CD and then rewrite it to a Mitsui Gold audio master blank disk, after treating the blank disk.
It's actually must simpler just to rip the disk and then play it back using a computer audio solution, like USB or Ethernet. I also makes your entire library more convenient and you don't have to listen to tracks that you don't like. Jitter will be much lower than any transport too.
Steve N.
Empirical Audio