Many thanks all for your help. The more I look into this the more of a nightmare it becomes. When I hear 'Triac' I shudder.
My customer has now pointed me to this, turns out he had it in his mind from day one, hence why he went DMX. For the sake of £50 I'll give it a go. ...
I have a hobbyist customer who is running multiple zones of DMX lighting from his PC.
He wants 'normal' switches to bring on, dim and switch off the DMX lights to override the DMX from the PC.
Anyone got any ideas?