Since the secondary channel has DMA turned on I doubt it is a SIS driver problem.
From the Maxtor web site:
Cable Requirements: An 80-Wire UDMA Interface Cable is REQUIRED for all UDMA/66/100 hard drives. It is recommended for all UDMA/33 hard drives.
This will probably stop you from getting DMA mode on the drive.
Other things to consider;
in the bios it is better to IDE detection to AUTO and let the bios interpret what is connected to each port.
If you are using cable select on the drives use the master slave pins configuration instead. Many people have reported problems with optical drives using cable select. I tried it on my Intel chipset board once... It only took once to never try that again.
Upgrading to Windows XP SP2 may help, no guarantees on that.
Remember to do just one thing at a time, otherwise you'll get lost on what didn't work and waste a lot of time and get frustrated.
Hope some of this helps.