Well that's weird behaviour in youtube and/or soundblaster

So my soundblaster let's me switch between speaker and headphones.
Just now I switched back to speakers, which means videos stop playing (I have to wait a few seconds then reload the youtube page in order to get the video to continue, I guess the player needs to reinitialise audio output). Anyway, Youtube just stopped playing audio completely for me. The video played, it was unmuted, volume all the way up, volume set properly for my speakers too, Chrome unmuted and at vull volume in the Windows audio settings. It even showed me that there was audio playing back in the volume mixer.
Kodi played music just fine, and a video on heise.de had audio as well, so wtf was going on?
Well as it turns out my soundblaster output was set to 5.1 surround. I don't know why it got set to that, it never has before. It also doesn't really explain why everything other than youtube continued to work just fine ...