The NAD T753 has plenty of power for your Totems. The T763 only gives you more power (more than most people need for surround sound)and video switching for the second zone output. The RS-232 port on the T763 only allows advanced control systems to be connected; not software upgrades. Be sure to get V2 firmware. It gives you much better bass mannagement and better second zone flex.
Good luck!
Good luck!