not sure if i've misunderstood, but the unit I posted transmits at a frequency of say 107.9fm which then you pick up on your FIAT headunit (107.9FM). So bluetooth from phone to unit and radio waves from unit to car.
Result is from the car headunit you get FM / CD, from the unit you get youtube/itunes/amazon music, DAB.
The unit needs a 12V supply from the cigarette lighter socket and also comes with a DAB aerial which you stick to your windscreen (self adhesive) and hide the lead behind the trim. It can be pretty stealth if you take your time.
The wife is well impressed. I've got one of those slim line Pioneer headunits in my Multi with USB and 3.5 jack in the front. It was about £50 and in all fairness the quality is better than the transmitter unit which now and again be a little crackly. But for £22 the transmitter job is hard to beat.