Maybe just convert a couple areas to mono and that opens up 2 conductors plus the shield. Put in K4's or whatever in these areas and have these control the other areas as well. In addition if they don't have an audio matrix put one in for true multi-room
One draw back is no VC in the areas you left as stereo or you could do the whole thing as mono and put in your RK3's or 2's everywhere. Mono is not that bad for background music or areas that the speakers have a lot of separation anyways.
On Video zones you could do zigbee remotes