the 950 is a pre/pro/tuner, basically it process sound. I.e. a signal comes from the dvd player, the 950 decodes that signal and process it to create your surround sound (or stereo sound).

the amplifier takes the processed signal and amplifies it, i.e. gives it power and sends it to the speaker.

If you wanted, you could get a good dvd player with lots of different decoding and an amplifier and skip the 950. There are some issues with that as well.

I am sure one of the others can better explain though.

Rich