You may be better off going with an entry level DAC. Something like an AQ Dragonfly should work very well for you.
4 responses Add your response
The jitter of the digital source is critical, more important than any other thing in a digital system. What you are experiencing is jitter. This can be reduced with a reclocker such as the Synchro-Mesh, but the cost is $600.
You are probably also using something like iTunes on a PC. Never do this.
On PC, you should be ripping CDs with dbpoweramp to .wav files and playing back with either Foobar2000 with Kernel Streaming or JRiver. Both of these are even better used with Jplay.
PCI cards all have relatively high jitter, even the $2K ones.