"tech from a national distributor " yeah that's a good one! Ask him why 1st off running a shielded 2 conductor in a 70V system somehow dictates noise rejection. Then ask him how exactly your are supposed to ground the shield and to what. Does he expect you to strap shield to ground at the 70V amp? Well while I can't understand how that will do you any good in that application, go for it! I couldn't even guess how many commercial 70V jobs I have done over the years but I have never done that or even have anyone suggest it. As far as running it with video in the distances your talking about I doubt the 70V speaker line will be the cause of noise, more likely the distance and or the cable itself. I don't think the shielded cable will cause you any problems so if it makes you feel better go ahead, couldn't hurt!