It seems really, really, inconvenient that the only way to load from a disk image on a Saturn requires a format that is used only by one proprietary Windows program. Is there *any* way to convert a bin/cue to .cdi aside from buying a copy of Discjuggler (and since I'm on Linux, booting to Windows)? If the format is simple enough that you need to use it as a format for disk images, surely someone has at some point written a simple command-line conversion program?
If you need that format for Rhea, then try using CloneCD instead. That one is nearly identical to bin/cue, just with a different descriptor - I'd find it much more likely that a Linux equivalent exists (I did not check however).
CUE/BIN does not necessarily include subchannel data, so should conversion tool fake it if it's missing? Other than this, CDI is closed, and while converting from CDI is relatively easy, generating valid CDI from raw data might be difficult if you don't know every field's meaning. If you're into writing tool like this, look at libMirage, its sources contains reverse-engineered info about CDI format.
Right, I got it backwards... a CloneCD image can also function as a bin/cue since main channel data is the same format. CCD of course has extra subcodes. However those can be "generated" from a Cue sheet, for basic P/Q subcodes. AFAIK the CDI format is just main channel + sub channel interleaved per sector, plus lead-in data also stored. However I did not look into it any further than this impression. You could also check CD Manipulator, which is open source (for Windows) and can produce CloneCD images.
discjuggler demo version is free and only limits burn speed and a data limit (think it was 700MB (this is not the size of the disc image but the data contents) but that should not be more than any saturn game), the demo does not expire so you can use it as much or as little as you like