Neilnewsgroup is on the right lines with a multroom set-up, but the
sort of switching and control functionality that Marc wants won't come
cheap.

Since there's no budget specified, and Marc is talking about using car
speakers instead of proper inwall speakers, then I'm guessing there's
not going to be a lot of cash flying around. Getting signals to the
different zones is going to be pretty easy. The hard bit is how you
control the sources when they're in another room in the house. You then
have to think about who has priority, The last thing you need is to be
recording off Sky and someone in a different zone changes the channel.

Marc, there are too many unknowns here for anyone to give you a
sensible answer. If you are looking at anything less that £5K for the
kit then my advice would be buy three separate systems.