Likely muted by default unless you have a license to the music you can just do what i did on my twitch.tv/craft and go to monstercats music channel on twitch they have a link here:
You can pay 5$ a month and play all monster cat music on your channel and twitch wont copywrite it as monstercat will link your license and account to twitch so you will be fine.
THIS is one example of what many larger twitch streamers do.
I just recommended what i do.
Hope this helps.
Unless a staff response is here i go by what i said i think there muting will not change as they dont want to be sued.