Great news! Glad to hear that all is working ok. I guess it must have just got a few bumps during delivery, adn cleaning/reseating everything sorted out some loose connection.
Never heard of IDE 99, but you can download IDEfix 97 from Aminet.
You should be able to use pretty much any modern CD drive, although dpending how fast it is, speed will be limited by the cheapo IDE bus of the A4K. This won't cause any problems with reading CDs, but if you were writing a CD you may experience buffer underrun.
Regards
Rich
EDIT: Is that the EIDE99 adapter from Elbox (kind of wedge shaped, socket on the bottom, two pin headers on the side)?
If so, the connector on the bottom is 44-pin, and will not physically fit onto the 40 pin IDE header on the a4000 motherboard.
Assuming you have only one hard drive in the A4000, you can just attach the CD rom drive to the same IDE cable, and set it as slave using the jumpers on the CD rom drive.