This worked for my Yosemite install after hanging on USB Sound Assertion.
I found the system caches told me that there was no plist for the FakeSMC, so I deleted it, along with the installed KEXTS from the output of kextcache -update-volume. Once they were all deleted (and would eventually be re-installed anyways later once we re-install OS X Yosemite 10.10.1)
Previously doing this install from Mavericks, I ran into lots of issues where the install failed etc. With the Multibeast kexts simply deleted (only threw them in the trash actually, just in case), the OS installed much more smoothly this time around. The install actually said it succeed this time, unlike the initial upgrade install I attempted. The first attempt was complaining about the inability to read caches, and said the install failed. I was able to boot into Yosemite, but that's when the above mentioned Sound insertion errors began. So I ran the terminal kextcache commands to see what was wrong, and after removal, the install of Yosemite finally finished successfully, and subsequent install of Multi-beast installed successfully (where it didn't before).
In summary, it seems that the older kexts that worked in Mavericks probably cause too much havoc to simply upgrade to Yosemite. Deleting them seems to make the process actually work. I also had done the DVD playback fix, which I'll need to re-do, that possibly caused some issues. It too is no longer working.
But we're up and running now. It was painful, but it's working now.
