Oh yeah, you could use 3.5mm to RCA as well.
Well, XLR would be best to use as it's a balanced audio signal, but only if it were proper XLR to XLR. You don't have that option from your sound card without going digital out to another intermediary device.
Just get a good quality cable and that will be the best you can do. I seriously doubt you could hear any difference at all, if there even was one.