External Sound Card for iMac...

First allow me to apologize if this has already been covered in another thread but I searched for about an hour and could not find anything recent on this topic. I'm also not sure if this is even the right sub-tab for this kind of question...but here it goes.

I just recently purchased an iMac computer and would like to use my existing Altec Lansing ADA995 200 Watt THX sound system. Here is the link for the specs of the system

http://www.overstock.com/Electronics...8/product.html

Now the system has one of those "Yellow, Green and Black 3.5mm jacks to connect it to the computer. I can hook it up to the Mic out jack on the back of the Mac to get base but cannot get any other sound from the speakers. I'm assuming it's because the Mac outputs a Digital Signal and the sub and speakers are analog. My question is would it be possible to purchase an external sound card that would solve this problem. Im not even concerned about the surround sound at this point...just the two front speakers and the sub up and running would be more than enough...

Thanks in advance for any and all help on this fellas...and once again, my apologies if this has already been recently covered and or it does not belong in this section.

Well, you solved my problem Ross and I can't thank you enough. I don't know why I was under the impression that the output on the Mac was limited to digital only but I am THRILLED to be wrong in this instance...

Again, thanks for taking the time to help me out here...it's very much appreciated.