Multi-Sub Theory

It's hardly the Theory of Relativity but I believe that this theory would make a significant difference to the effect of a home theatre.

From What HiFi's Sound Advice Pages on Subwoofers.

The whole point of a well-sorted sub is that it just sounds like your main speakers have greater bass extension. Oh, and better imaging and greater three-dimensionality. Disconnect your main speakers and it'll seem strange to you that the almost imperceptible murmurings from the sub can make such a difference, but they do.

So obviously bass extension on your main speakers is a good thing, however having a dedicated LFE channel subwoofer doesn't always mean the sub will be chiming in to help out your main speakers in the bass department.

For example when you have a surround receiver (specifically Yamaha's can't comment with any great authority on any others) setup in stereo mode and your speakers set to "Large" the Subwoofer on the LFE channel isn't fed any signal. Obviously you don't want to set floor standing speakers to "Small" and reduce bass signals going to them altogether. The same holds true when you are in Surround mode, there are often cases where signals similar to that driven to the LFE channel are present in the other channels which would benefit from the additional drive of a Subwoofer.

This got me to thinking, higher end receivers/processors have pre-outs which allow you to connect additional power amps to the system. These could also be used to drive active subwoofers with built in crossovers. This would give you the low end drive in your music in Stereo mode as well as an additional kick in Movies.

The same theory could be applied to other channels in the surround setup as well, allowing you to have a dedicated subwoofer for centre and surround channels.

Of course I'm still on a technology ban so it will remain an untested theory for some time :)