Sound Blaster to Audiophile DAC - options

I'm playing around with this idea of using my HD as a transport and a decent quality PC sound card as either my on board DAC or, as the output to an audiophile grade one (e.g. Mark Levinson 360s).

The sound card I'm currently using only has mini-jack outputs but, one does support either S/PDIF coax or, analog. I'd like to try both (just to see how different they sound). I can use the analog link, direct to my pre-amp, with an older Monster Interlink 400 Mark II mini-jack to RCA cable but, to make the S/PDIF coax link to the ML 360s requires a mini-jack to singe RCA adapter.

My question is, does anybody have a good recommendation for this or, is there a high quality cable out there that is designed for just this purpose ? I expect the PC card linked to and external DAC to really deliver 'the goods' so, I'm hoping there is a good option here.

In case there are any questions about my current system:
- McCormack DNA-1 Platinum
- Foundation Research V6 (tubed pre)
- Mark Levinson 360s
- Infinity Renaissance 90’s
- Valhalla IC’s
- Foundation Research LC-100 PC
- Foundation Research LC-1 PC
- Harmonix X-DX Studio Master (Wattgate) PC’s

Thanks,