Almost Portable MuseScore 3

Since there is no portable version yet, I thought I'd try to beat the system. I just copied the whole MuseScore 3 folder from my PC where it had been installed normally onto a usb drive. When I then copied that folder from the usb drive to my other computer where I need to use portable apps, the program works just fine. Except. I cannot enable the playback of my scores.
The Synthesizer box is greyed out when I try to see where it's looking, and restarting MIDI and audio didn't fix it, nor did resetting to factory settings.
I can still export to mp3 (which seems a bit odd to me that it works), so I can hear what I've done, but it would be nice to have it work in the normal interface.
Any ideas of what might be needed? Maybe there's another folder somewhere that I need to transfer as well?
Thanks,
Charlie