You can assign the music accessible to a sub-user from the Users tab:

Then choose the user and click "Assign music":

From the pop-up window, you can choose which playlists, mixes or schedules are available to your users by clicking the checkbox on the far right. You can filter by stations, mixes and schedules by using the filters below the search bar.

Clicking on the "Autoplay" button will make that selection play on a SoundMachine player, or by logging into the web. 

You can also choose the playback options for autoplay by choosing Full, Mellow, or Upbeat when setting the autoplay setting. 

To remove a playlist from a user account, uncheck the right-hand box. 

You can also assign music to multiple users in bulk by holding shift and clicking each user you want to assign music to. After that, click on "Bulk Assign Music" and follow the same steps as before.