SCSI was once the "king of speed" with data. And flexibility to work up to 7 drives, even read/write factions simultaneously.
But today, the SATA class has put it to second level.
Indeed you can run a SCSI drive system alongside an IDE or SATA system.. as long as the DMA assignment is different than the parent host if on the same IRQ. But preferred on another IRQ intended for its use.
Reference chart:
http://www.pchell.com/hardware/irqs.shtml
Check the date of manufacture on the optical drive. If more than 5 years old, it may have a foggy coating on the laser lens, and that could affect its operation. Very mild hand soap, 1 drop per tablespoon, may be used on a cotton swab, very gently. Best is a dry swab, still being very gentle! Never use cleaning solutions containing ammonia on polycarbonate lenses, as this can permanently yellow them.
And
NEVER, EVER power a laser disk drive with its cover open, as you may blind yourself in seconds. The beam is invisible!