It can be done, but it's not what you're thinking. When you rip a CD in your computer drive you are generating a computer file (AIFF, WAV, MP3, etc.) while the output of your CD player, assuming it has a digital output, is a PCM data stream. It's possible to output the PCM stream into your computer using a software recording program which in turn would generate a computer file which can then be directly accessed by iTunes. To do this you would need a digital input on your computer. I suspect this method would generate a far amount of jitter in the signal. You would also have to do in real time.