Hi Chris, as you rightly said, Carrozeria, is the Jap version of Pioneer. By your description it's an FM modulator CD changer, probably due to the complexity of changing the radio in a Soarer.
Assuming they have worked ok together in the past, it should just be a case of retuning the radio to the output of the changer.
As has been said already, try a pre-recorded CD in the unit first. If the unit is more than 3 years old, it wasn't designed to play CD-R's, (they usually do, but they weren't designed to).
If you can't get it to tune in, check that a frequency expander hasn't been fitted which is stopping the original radio from going down, (oo-er), low enough to pick up the signal.
If you know where the modulator box is, they usually have either a variable control or multi position switch to change FM frequencies in case of another radio station sitting beneath the CD when playing - This should tell you what frequency you're looking for.
If all else fails, I think, (going by memory), I can get a complete new one for around £125 + Vat. - UK units work around 88-90 mhz, so you'll be able to recieve this frequency either way.
Good luck:)