Hey all adventurous OS 9.0.4 users!
Ok, Here's the deal, if after installing OS 9.0.4 and you find out that you CD Rom drive does not mount and CDs, here is the cure:
First, start by restarting your machine with you OS 9 cd in the drive (note: do not try and boot to the cd, just let the machine boot as normal). Now, your OS 9 cd SHOULD mount. Next, remove the Apple CD/DVD driver found in the prefences folder and place it in the trash. Finally, install just the Apple CD/DVD driver from the CD, found in the custom install under OS 9 then multimedia.
That is it! This SHOULD work, it did for me. I wish you good luck, and maybe next update this will not be a problem.