I came upon the solution through logical thought. Thinking about the lousy software that comes with the drive that I'd never installed I remembered Veritas had a lite version of RecordNOW on the disc. I installed it thinking it might update the engine so that the DRU-550A could work with PrimoDVD. Unfortunately it didn't, but in further curiosity there was a link to RecordNOW MAX in the program encouraging you to upgrade to fully fledged software. I decided to bite. On the page for RecordNOW MAX it encouraged users of not only the lite version to upgrade but PrimoDVD users as well, so I thought that might be the key. I downloaded the demo and what do you know, it just happens to work with .gi files as well as the 500A. So, mystery solved.