help choosing cable pc to dac.

What model of DAC are you using?

Perhaps you can use a usb to Spdif converter and run a single length of RCA.  I used the Musical Fidelity V-Link to this end a while back.  This way you still get USB out, which can be a benefit, and run a good signal through the lone RCA.

Personally I wouldn't go crazy on the cable. I'd look for an entry level cable by good manufacturer to connect to the musical fidelity v link.  I would definitely not use the 3.5mm jack.  USB will be far better.  The Cable Co. Has custom lengths available for Kimber V21 digital coax with RCA connectors.  That will cost you $149 for a 5.5 meter run.  There is a V-Link II on Audiogon now for $90 which will handle up to 24/192, so that's a steal!  Pick up a short high quality USB cable such as Kimber's USB Cu for $50 also from The Cable Co.  Total expenditure $300.  Pretty high quality stuff, and getting the benefit of USB out of the computer is great.  Good Luck!

Was the v link and lengthy digital RCA cable out of budget?  Unless I missed something, you could go USB out, translate into SPDIF, and into the coax input on your DAC. Couple hundred bucks, problem solved!