Days later: Haven't gotten very far with anything at all unfortunately.
Contacted the fellow that wrote nanowasp emulator. His reply :
>In terms of tape formats and sound - I don’t think I ever got around to supporting sound output in
>any of the emulators I wrote. A long time ago someone did fork one though and created uBee512,
>which is much fuller-featured than mine. Perhaps this is the one you’ve found?
>
>I’d guess that it probably just requires a file with the raw bytes that would appear on the tape.
>If you take a look at the code here you’ll see the what the format looks like:
>https://github.com/dgchurchill/nanowaspjs/blob/master/src/virtualtape.ts#L140-L196
>
>Roughly it’s a header, followed by a simple checksum, followed by 256-byte blocks which each have
>a checksum. (see
>https://github.com/dgchurchill/nanowaspjs/blob/90ecdb01f897bac4830ad5902105956a8e5e3e05/src/utils.ts#L276
>for how the checksum is calculated)
>
>I believe you should still be able to find Stewart Kay (author of uBee512 emulator) at
>https://microbee-mspp.org.au/forum under the username uBee. There’s lots of good info there too
>about his emulator, and there may be tools for creating the tape header.
...I'm on to it.