Ugh. An older version of Airfoil and I guess in particular their Instant On component really messes up in High Sierra. I can't say for sure, but I think it was even choking Safari to death; pages wouldn't load, although sometimes it depended on the page. Sometimes I got almost nothing. And the Sound Pref Pane wouldn't even launch fully. And no sound, and coreaudio failing per Activity Monitor. Suspicious, I launched the older version and could update within High Sierra, but several attempts to install the Instant On upgrade, or even uninstall the old one, resulted in hangs. And BTW, you have to force quit from within Activity Monitor. I manually found the components and launchdaemons in /Library, and got rid of them, and stuff seems to be better. And on a laptop where I had upgraded Airfoil BEFORE HS it had no problems.