Hi.
From the modem point of view, the engineer will have to split the Cat5 cable, and feed one to the new modem, and the other to the V+ Box. You will have a new account set up, and your original emails will have to be migrated to the new account, this should not be a problem at all.
Your modem will need to be connected to the router, the ntl servers will then learn the router MAC address. I'm uncertain if you will need to go through a set up process via the autoreg system. Everything should be OK.
I can't answer your question about the HDMI connection, but I am sure somebody here can help.
Good luck.
