The power rating doesn't matter much, it's the gain of the power amp that matters most. The power rating gives an indication of the maximum sound pressure you can achieve, where in this case the 216 will be able to achieve a higher max. sound level than the other 3 channels.
I'm not sure the 216 has an input level, but if it has, you'll have to adjust it with a test tone so the sound level matches centre and rear. If the 216 hasn't got an adjustable input, you have to change the level of centre and rear channels so they will match the front. This can probably be done through the menu of the T753, check the manual for that.
Either way, it would be handy to have a device to measure sound pressure and maybe a good test DVD. They won't cost the earth, but will be of great help setting up your system.