If you're going to use a 70V system, you aren't looking for audiophile quality. The signal is already running through step-up and step-down transformers, so a little more inductance isn't going to make a noticeable difference (IMHO).
I'm not sure how much effect it might have on EMI/RFI either. I suspect not a lot. I would be more inclined to put a twist in the cable, keep it away from mains as much as possible - and when you did have to cross a mains cable, do it at right angles.