The good news is you don't need an .rge to .pst converter to get your email files into Outlook, which tend only to run on Windows. You just need an .mbox (or Mail) to .pst converter. There are some available through the App store. I trialled "Mail To PST Converter" from the developer and it worked fine for Outlook 2016, but that is just one example. I am sure there are others out there if you search for them.
Yes, all .dbx are ok!The .sbd should be used by an older version of outlook express around 1998-2000.The .sbd are folders and there is in the same directory the name of the .sbd directory without extension. Opening a .sbd I see other .sbd directories (the subdirectories in the e-mail client) and the name of the .sbd directory without extension. I'm not so sure that the files without extension are .mbox files but it's possible to open them in text format with gedit and read in a quite way the e-mails contents (unless the attachments).Now I attach some images of the .sbd directories and files...Thank you