I am a bit disappointed that I did not think of this myself. I mentioned a few days ago that I was about to order an FM transmitter so that I can play MP3s through my Jaguar stereo, since I only have the single CD player in-dash. It is about $1000 to have the Jaguar disc changer installed, and none of the aftermarket stereos seem to be capable of working with the steering wheel controls.
One reader pointed out that you can record a lot more MP3s onto a CD-R if you do it in data mode, not audio mode. In audio mode, it acts just like an audio CD. In data mode, the files are stored like a computer disk directory and at much higher density. Many newer CD players will play data CD-Rs. As it turns out, not my 2005 Jaguar, or the 2007 TrailBlazer, and I did not even try the 2000 Corvette. But there are CD players around the house that will play the data CD-Rs--and I can get about eight CDs on one data CD-R.