If you need more flexibility you can get Spanner.
http://www.thecargocult.nz/spanner.shtml
I don't work for them, by they way. The only drawback with it is that your sends must match your output, so if you use Spanner to turn a stereo into a 5.1 then your send has to be either 5.1 or mono. Without spanner a stereo track can have a 5.1 output and a stereo send. Also you have to get used to your pan info being plug in automation, not pan automation. Changes your workflow, but add many up-mix and down mix options. Plus has cool iPad app.