I've got an older Onkyo amp. TX-sv727 that I'm trying to hook up to my mac, so I can do things like play itunes through the amp. and the speakers hooked to it. I've read that you can use a 3.5 stereo mini phone plug to dual rca jack stereo cable, to do this. I've tried it and it doesn't work. Is it possible to do this on a non-digital unit? Is the magic in using a sound card?