Ok, so changing my system definition from a Mac Pro 5,1 to a 3,1 fixed the crash on boot, but I have no internet. Have never needed to use any special kext for Internet in the past (motherboard is a p8p67 pro v3.0), is there something different in 10.9.4?
Edit: And no audio, but that's a smaller concern at the moment than the Internet. Network control panel shows that it detects the cable is plugged in, but the system doesn't have an IP address.
Edit 2: Audio working using alc892 fix from an older version of multibeast. Tried an Apple USB ethernet adaptor I had sitting around, still no luck. Same message about the cable being plugged in but not getting an IP.