Actually, they should all be master! That's why I got a SCSI CDRW, so the DVD and HDD could both be masters, and the CDRW would still get a constant signal. But you could also get a PCI IDE controller. Then you can make them all masters and have plenty of places to put an additional drive, such as a zip, backup hard drive, etc. In fact, if you bought a RAID controller, you could have it set up as the boot device, and RAID some drives on it, and then use your onboard controller for the CDRW and DVD.
Cast not thine pearls before the swine