tony sayer wrote:
The room's about 4 metres square, by the way, with a concrete floor
which will be carpeted, and thick stone walls.


What ever you put in WILL be wrong!

How much wrecking are you planning on? is there depth in the wall and
space to fit buried conduit and some draw wires? Then either you or
whoever fits the system could pull their own cables through when needed.

Excellent idea if you can do that...
I always advocate lots of buried conduit. You can get flexi in all
diameters from 12mm to 50mm. 18 or 25mm is OK for most jobs. Put draw
wires in. Terminate in deep steel patresses (backboxes) set into the
wall. Cover with blank plates until needed.

Bill