Trying to identify the spec/format for datafiles with these markers

Question

I'm working with some binary multichannel data logger files, and I'm finding the following plaintext markers all in the header of each file for a given logging session:

• RDX
• PPX
• IIX
• MMX
• GGX

I swear I've seen these before in a legacy database format, but for the life of me cannot place where.

• Having no luck on DDG or Google, just keep getting autogenerated "filetype" website results...
• Went down a rabbithole re Borland Reflex and Paradox based on some obscure link based on the RDX marker; they don't grok the format even when the extensions are changed for those systems. (Admittedly was kinda fun standing up a Win2K VM to test though.)
• Github searches yield no results other than base64 encoded content and 3-gram tuples in language models.

Anyone have an idea?

Thanks!