The cards Dean is referring to are made by San-Bar. Same deal, I don't think (I could be wrong) you could just connect the same music source to all the cards. Same cross talk will occur. San-Bar also made a 4 inch card that was a little radio on a card and the music came out on two of the pins that you could cross wire to the corresponding pins on their line cards. Again, it wasn't a simple plug and play. I think the music came out on 3&18, which is normally wired for A battery. Plugging one of these cards into an unmodified card slot fried it instantly. You had to unwrap the leads from 3&18 and insulate them, then wrap new wires from there to the card(s) you wanted music on. I've never seen one of these in person so I could be completely full of it, but that's what I've gathered from guys who've been doing this longer than I have.