I got Logitech's x-540 speakers for christmas, which is a 5.1 audio system. I have the last generation 15" MBP and there is only the headphone slot, so I can only play sound through 2 speakers, unless I use the active matrix feature which simulates 5.1. Is there any way I can play true 5.1 or do I have to upgrade the sound card? Any suggestion if for a sound card if I need one?