Same issue.
-Version of Boom: 1.9.4 (not Boom 2)
-System and OS: Yosemite 10.10.3, 2015 MacBook
-Problem occurs after every system restart
-using optical output and built in speakers.
Having the exact same issue -using boom 1.
App crashes and hijacks output. Can't seem to toggle away from "boom device" in sound settings either without relaunching the program.