Hi Petey

You can use flopy for upload sounds.
Web is full of factory and other ROMs "copy-to-floppy" format.

You can load complete banks.

Interesting thing is Native Instruments FM7 software synth. It emulates DX7, sounds even better.

You can use DX7 PC-editor and send sounds via MIDI to your synth, complete banks or individual sounds.

I know that because I had DX7, now I have SY99, it's compatible using PC-software editors.