If you dont want to change the DAC, then the next step is to insure that you have a good ripper and good playback software. Good rippers are dbpoweramp for PC and XLD for Mac. Good playback software is Amarra 2.3.2 (4317-19), Pure Music or Jplay for PC.
These will not improve on the master clock jitter, but they will insure that the data is delivered intack.
Then, third-order effects for improvement include putting the OS on a SSD rather than spinning hard disk, improving the PC power supply and eliminating extraneous applications.
Steve N.
Empirical Audio