Ok, after a lot of trial, error, and testing (thanks for all your help, Blondebeard!), I can finally say that loading, playing, and saving sounds now works, both from Thimbleweed Park .ogg files and RtMI .assets.bank soundbanks, on Windows, Mac, and Linux.
I've also fixed an error with saving RtMI's ktxb images, and I made the 'filter' field case-insensitive for all platforms, not just Windows. Plus, there's now a pre-built executable for MacOS too. Download version 0.1.3 here!