So, in the end we did it last night and he would get no signal on the F5 every now and then and the original box started to do strange things like jump in to the menu's all by itself etc so he has disconnected the original box as that will expire in a couple of weeks anyway :-/
We did not bother with changing the orig box to single feed only either so just left it on with the F5.
Thanks to all for their input, appreciate it.