Hey J, sorry your still having probs mate, if you cant get the line in to work there are two other options although both have drawbacks.
Get an fm transmitter. The cost and quality of these varys quite a bit, but basicly you plug it into ipod, tune it to a frequency, switch on your radio (fm) then tune radio to same frequency. Your ipod will be playing through your radio.
or
Get a cassette adaptor. The cost and quality of these varys quite a bit aswell, you plug into ipod then shove the cassette in your boomer and press play, downside being the door may not shut properly.
Both these items were fairly cheap on ebay, fm trans about £8, the tape adaptor about £3. but both are low quality and well, you get what you pay for.