I've had an Aurender N10 for a year or two and have tried all of its digital outputs.With that player, they're all pretty good. To my ear, here is the stack rank from best to not-so-best:
XLR: quietest with the biggest soundstage, great midrange & bass, and most organic sounding (what I use all the time)
SPDIF RCA: very, very close to the above
Optical: not a very deep soundstage, kinda "thin" sounding, but surprisingly good for optical
USB: not as good as any of the others, but OK
I have limited experience with brands of cables and currently run all Shunyata Sigma cables in my primary system save for the speaker cables. I'm sure that there are many good cables out there, but I worked up the Shunyata product line, so haven't tried others.
XLR: quietest with the biggest soundstage, great midrange & bass, and most organic sounding (what I use all the time)
SPDIF RCA: very, very close to the above
Optical: not a very deep soundstage, kinda "thin" sounding, but surprisingly good for optical
USB: not as good as any of the others, but OK
I have limited experience with brands of cables and currently run all Shunyata Sigma cables in my primary system save for the speaker cables. I'm sure that there are many good cables out there, but I worked up the Shunyata product line, so haven't tried others.