Well Many Isos that are downloaded from the web are in iso and mp3 format (for quicker download) and you have to convert the mp3s to WAV files to make it playable, I would think a turbographix game can be made the same way as a psx iso i.e. Isobuster or CDRWin, I say these because you can use a cue file to be used with bin files in case you want to use it in an emulator(Isobuster creates cue files for a img file (img is another word for bin and img, confusing eh?
) There is someone that is a lot more in the know then me in terms of PC engine stuff, so I'll try and refer him to this inquiry.