Did you do ALL the steps? If your bios does not allow AHCI mode to be turned off then you are not going to get this working. Note that the article was last updated in 2007, and hardware continues to move on so as time passes, you are increasingly unlikely to find that hardware continues to offer any backward compatibility with DOS.
In my opinion using PCDOS based boot software on modern hardware is mostly a waste of time. You do not mention in your posting whether you are using GSS 2.5.1 but assuming you are, the option of building a WinPE based boot device is also available, and is much more likely to work with SATA optical devices.
If you have an older version of GSS, you can build your own WinPE boot devices using this article: https://www-secure.symantec.com/connect/articles/readyadventures-winpe