That's probably not a good question to ask then if you are concerned about electrical isolation.
That depends much more on the exact DAC and interface used from media player/HTPC -> DAC.
For a simplified example, toslink automatically removed the electrical isolation issue but leaves much to desire on the jitter front. A regular BNC 75ohm coaxial cable will do much better at the jitter front but does carry the ground over. So if the DAC and media player has a good noise rejection circuit with a decent power supply, that would be prefered.
Regarding signal/noise issue on wired and wireless, any decent Cat5E ethernet cable system is great at noise rejection. Cat5E can transmitt 1gigabit/sec over 100ft easily without signal loss. That's far greater bandwidth than any DAC at 24bit/192Hz and any existing Wifi Network.