I believe in analog cable material differences (silver vs copper) as there's attenuation differences, but digital is digital, doesnt matter what its made out of. A bad cable is a bad cable, but with digital, as long as the data gets from point a to b...
I suppose an unshielded cable could produce some noise downstream, but the cable would have to be particularly cheap.
Anyways!
I'm still deciding on a portable DAC/Amp. Just something to keep in my bag with low output impedence, as my Shures are only 9 ohm.