<font color='#008080'>Yamaha is the only company that employs this type of DSP (that I know of)
FES are mounted above and outside of your mains.
When engaging Yamah DSP modes like 70mm Cinema, etc... the receiver sends a fixed bandwidth (amplified) signal to these speakers. Generally, these speakers are between 25W and 45W/channel.
The effect is a larger soundstage. Yamaha remotes allow you to easily and instantly switch between DSP and normal 5.1 modes, so you can tell the difference immediately if you can ever get to a system having this setup.
Yamaha calls it 8.1, but it's really a 6.1 + 2 receiver.
I wouldn't trade the effects channels for anything, as they truly enhance the movie-going feel of DVDs. I used to be a purist, utilizing no DSP with only DTS and DD, but now its crazy not to use the Cinema modes on movies.</font>