Can't set up 6.1 Surround in Speakers Config

I cannot in Audio/MIDI Setup setup -> Configure Speakers -> Multichannel setup anything, except Stereo (everything else is disabled).

I have iMac Intel Core 2 Duo. Do I need something else? I am connected via Digital Output to my Amplifier.

Thanx for any help.

You would need an external sound card for surround sound. They work off the USB ports. Something like this...

http://www.hometheatermag.com/htpcs/107griff/index.html

any more suggestions

Ok, thanx, I thought I might have needed sth like that, do you have any suggestions? except this one, or basically that would be the best option?

thanx

I don't have any suggestions. I don't even own one. I only know of these from doing research into using a Mac Mini in a home theater system and I haven't done that yet. You could go with an Apple TV. They support surround sound but then you don't get all the functionality of a real system.