Dave
As the above statement implies, your Sony CD changer is either dedicated (only works with Sony head units) or RF modulated (works with ANY FM radio). You need to ask your friend which one it was if you are not sure how to tell the difference yourself.
Once you figure this much out, weigh out your options. Depending on your current sound system, you may want to take a look at Sony head units. I personally am not too fond of the brand, however they have powerful internal amplifiers. Should you choose to purchase a Sony CD player and have it power your speakers (bypass the factory amplifier), I think you will be generally pleased with it's powerful sound quality and functionality especially with a changer in the trunk.
If the unit is RF modulated be aware you will lose a small amount of sound quality by sending the signal through your radio frequencies. However, like I said before, depending on your sound system preferences and financial situation, you might find an added CD changer will make you smile when all you have to do is hit 1 button to access another CD.
Good luck!