Thank you Mushii. I shared all this with the electrician and he honestly said that he doesn't know much abt AV and agreed to your suggestion. Thanks again for helping out.You could run a single cable to a switch, yes, but then you have another device to plug in with distracting flashing lights on it and generating heat in the AV Cabinet. Better to have a switch by the router and run 4 cables from the AVR to the switch.
305m of LSZH Copper Cat6 is currently around £100 - 30p a meter. Time to run 4 drops as compared to one drop of Cat 6 - the same.
Also always run 2 drops of Cat 5/6 to a wall outlet, never one.
Do it once, do it right.