Exactly - noise being AC will also cross the transformer to some extent, but ground-wire-bourne stuff won’t.
Paul’s comments about keeping the streamer’s computer-type noise is correct of course (though there has to be some noise etc. from whatever then converts that optical air gapped link back to I2S or whatever?).
Me, I like TOSLINK, despite its limitations, but also still wish a better optical interface was available:
@Paul - are there details available on why the ATT / glass fibre dev work wasn’t practicable?
Edit - this thread suggests cost
So I’m sticking with AES where available and TOSLINK elsewhere (and a bit of RCA SPDIF if necessary).
192 kHz over TOSLINK seems fine (passes bit perfect tests) on every device I have (that understands 192, some of it is 96 max) and is generally followed by reclocking / jitter suppression of one sort or another) 
I have recently decided to not bother any more with 384 / 768 as that requires USB and that just feels wrong 