The tape recorder isn't in use. Where would I get that iPod adapter thingy ? Best would be to get to know which DIN pin is connected to left, right and ground in 3.5mm jack as I could do it myself...

So, I have an old Beomaster 4500, and I'd like to get my computer connected to it. I have an old tape recorder that we don't use, and it had these 7-DIN -> 4xRCA connectors in each end. Does anyone have the pin order I have to use to get audio from a 3.5mm plug from my computer to those RCA connectors? I've tried to fiddle with it, so