Since you don't really have any control wire to speak of for control, I would use hand held remotes with zigby that way you don't need to worry about antenna wire. Most of our larger projects usually only have 2 maybe 3 K4's the rest is individual hand held remotes. some times we use K3's but not always. forget 2 way for this job, Just focus on getting a decent matrix switcher, the Knox mentioned is a good choice, the commands are already in the data base, if the 12 channel amps he has a decent keep them, you have some equalization available with the Knox to make them sound better, if they are crap you can use the B&K or Audio Control or whoever you prefer. As mentioned above it is possible to sum the grounds on a 4 conductor for a pair of speakers, this will leave you with a free conductor and the shield which you can use as Signal for a touch panel, if you can get local power to the touch panels, you may still be able to pull that off. From what have told us, this really does not sound like a very difficult project, because you have to work within your limitations, and the customer has to understand this, If you want to do distributed video, and there is at least available cable at every location then there is a possible solution there as well, since there is a product that encodes up to 255 devices over a single cable run, if your customer is willing to pay for it,then that can be done as well.

No problems only solutions.  don't look at the whole thing as some mountain you have to climb,  break it down into smaller parts. Put it on paper and walk through it step by step, think outside the box and you will succeed