I was to join mp3 (audio) folder on my emby server but it doesn't work. There was already an folder with movies. But when i put the mp3 folder i cant see the mp3's. When i deleted the movie folder and did the mp3 folder first and afther the movie folder, it works fine for me! maybe someone have the same issue... so here the solve in emby webclient:
1. Delete ur movie folder
2. Put your MP3 folder named music or els
3. Then put your movie folder back.
Hope you enjoy this