Hi Earthquake:
There is nothing wrong with the NAD T743 and it would work fine with the EPOS M12i. When you begin to move up to seriously better equipment though, you will begin to notice the ceiling levels of your other equipment. It just happens as your ears get trained.
The T743 is a HT receiver. Are you using the NAD in a multi-channel set-up, or are you just using it in a 2 channel mode? If you are using the T743 in a 2 channel mode, you could probably do better for an amplifier in its price range ($800 or so).
HCM Audio has a demo pair of the EPOS M12i for $900, which you may wish to check out.
Best regards,
Rich