Russ,
A few brain cells just kicked in and I want to clarify some earlier info and add some.
First of all, when I mentioned putting the burner on the drive carrier my brain was on vacation. That would be OK for a hard drive but not a burner since the media needs to be ejected.
You would have to either replace one of the upper drives with a bezel (like the present CDRom) or move your extra hard drive to the carrier below and use the sled/shelf of that drive for the burner (just below the zip).
Here is an illustrated instruction page for replacing the CDRom with a burner.
Install burner in 9600Yes, the IDE PCI card will allow you to run the burner but there are some caveats. Depending on the card and burner you may have some problems with playback in the burner if it is in addition to the CDRom that is now there. Sometimes only one audio source is recognized. (There is also the possibility of a SCSI to EIDE adapter which would attach to the drive and then to the present SCSI connectors and then you would not use a PCI card.)
Do go
HERE. Enter the search info CDRW, EDE PCI card (interface), 9600, 9.1. You will get several reports on various peoples experiences. Note however that many are older and won't apply to the more recent burners and cards. It will give you an idea of what may work or what problems you may encounter.
The more I think about it, for simplicity and ease of installation, the external FW burner would be most appealing to me.