I've now found this kit by the US company Monoprice:

http://tinyurl.com/j5dy6he

or in full:

https://www.youtube.com/watch?v=0AKm...?v=0AKmFXPnGRw

That's a YouTube link. Ideally for my purposes this is an audio amp as well
as a six-zone speaker distributor, and it comes with very neat wall-mounted
remotes which allow switching of input source, output zone and volume -
everything I'm after.

It's a pity that it's only available from the US since that pushes the price
up, but the kit gets some very enthusiastic user reviews and the company,
which was new to me, seems to be a respected one.

So problem solved, I think. Many thanks to everyone for the thoughts and
suggestions.

Bert