You may have seen this posted somewhere else before but a NEC 6100A is the OEM version of the NEC 6500A retail drive. The same drive.
Your problem is not that your drive doesn't work, but that it doesn't recognise certain types of media. There is no conceivable reason you couldn't flash to one of the Dangerous Brothers versions of the firmware for the 6500A that may be more up-to-date with regard to media types, but I don't know how "new" the 203D version from Dell is. You may get more insight by visiting the Dangerous Brothers website (or somebody else here more familiar with the different versions can speak to that issue).
This page (http://www.micheldeboer.nl/firmware/6500.html
) shows the relationship between all the versions, the specific features of each, and the release dates. It would seem that the 203D version is the latest, if not the greatest. I read somewhere that Dell gets their releases early, since they are such a large buyer of NEC drives.
I may try TDB's 2.24 though. I find the whole thing quite frustrating, since I don't want to be a power user about this stuff, I just want to make backups of actual data (and not even rip movies), and I have an ever increasing pile of unuseable (to me) blank media. Rrrrrrr.