[brucek]

To me, all the questions about adding extra subs can be boiled down to a single truth. If the subs will be sharing signals that are at the same frequencies, they better have matched responses or there will be a problem.

I don't really understand the rear channel sub. If the rear channels are set to 'small', all the low frequency information will be directed to the main subwoofer. I suppose if the rear channel speakers were challenged and couldn't extend their signal down to the crossover, a small sub that reached to the crossover could be added with a speaker level connection.

Besides the obvious fixed location problems with built-in tower subs, there will be an extension limitation to your system if the standalone sub and the built in subs don't have identical bandwidth capabilities. One of the biggest problems with built-in tower subs is getting the user to run them in 'small' mode when they add a large standalone sub to the system.

brucek