Three CD-players were available. Bavaria Electronic CD (658), Bavaria Electronic CDII (659) and BMW Business CD RDS (replacing 658).
The first ones came with a CD cartridge where you put the disks in and then into the CD-player. At least the CDII also needs the HiFi-system to work properly. Business is more modern and does not have that cartridge and works without HiFi speakers (676).
Of course there are many newer versions that will work as well, but these were the factory ones from BMW.
If you do speak N/S/DK language most units are found on photos in this thread on the Swedish board (login needed first):
http://www.e34m5.se/forum/topic.asp?...&TOPIC_ID=1804