Realtek ALC889 SPDIF out or get a USB--> SPDIF out to DAC?

[GamerStudent]

So I'm purchasing a DAC soon, and the DAC will not have a USB interface, this leaves me with either using the onboard realtek ALC889 Coxial or optical out to the DAC or purchase a USB to SPDIF unit.
 
Now because I'm keeping a digital source digital, I'm not too sure if the quality of the soundcard matters or not...which is why I'm asking. Please teach me!

 

[necropimp]

quality of the sound card matters little when using digital out... as long as the 1s and 0s are passed through that's all that matters

 

[Roseval]

Digital audio on a computer is PCM (Pulse Code Modulation) audio.
It are samples (the bits) taken with a fixed interval, the sample rate.
Play back is converting the bits to analogue and this must be done with the right sample rate.
To generate the sample rate you need a clock.
A clock is an analogue device; precision can be very high but never perfect.
These tiny variations in the sample rate are called jitter.
If jitter becomes too high, it becomes audible.
The bits might be perfect, the timing will never be.
 
So the question is how does the quality of the timing of ALC889 compares with a USB > SPDIF converter.
 
A simple introduction: http://www.dcsltd.co.uk/page/assets/dCS_Guide_to_Computer_Audio.pdf