Yes as I had explained at first it was exactly that, a playlist stored as MP3s on my own server. It has been running that way for 5 or 6 years now. Something has changed recently and turned off this ability and we lost our ride soundtrack. But using sound media makes sense rather than forcing MP3s into the parcel music stream. I also had a music player on my parcel which used the same system to make a parcel playlist stored off in the cloud. That wont work now either.
But using a similar system by sending the mp3s to the default media will work, so if anyone is still selling these sort of devices then at least it has a fix.