I was thinking about placing a 7500 at the rear of the room and using 4 channels for the surround and one channel for the sub, which is also at the rear. As I understand it, I can feed the sub with the balanced output and use the 990 to set the x-over independent of the settings for the other channels. Is that correct?

However, if I use a plate amp to drive the sub, I will give up balanced connection (I can't find a plate amp with balanced input) but I will gain the ability to adjust the phase of the sub.

Isn't having phase capability important?