Did a little test, here is the setup.

I used a Dolby Stereo DVD, Andrea Bocelli "A Night in Tuscany." There is a part near the end of "Nassum Dorma" that uses kettle drums. Now, the speaker system does reproduce the kettle drums without a need for subs, but every little bit helps. I had to look at the LED's of the sub amp to detect if they were getting a signal.

And the results were...

The only configuration that produced a signal at the sub was 5 channel stereo through the analog connection. Any other configuration through optical or analog with Stereo, Dolby, PLII-C, NEO:6, Dolby PL did not produce a signal at the sub.

So with the speakers set to large you can get output to the subs if you use an anlog connection in 5 channel stereo. I posted this before I read the previous two responces.

I am going to try and set the main and rears to small and see how that goes.