HAXM silently crashing on OS X 10.9.5

Installed latest version of HAXM manually on 10.9.5 with latest version of Android Studio.

BUILD SUCCESSFUL
Total time: 14 seconds
Built the following apk(s):
    /Development/todo-lite/platforms/android/ant-build/CordovaApp-debug.apk
WARNING : no emulator specified, defaulting to Tab_S_style
Waiting for emulator...
HAX is working and emulator runs in fast virt mode

There's nothing logged in the console/system logs at all.

The emulator window opens, stays blank (whether I check use host gpu or not) and doesn't boot. ADB shows it as 'offline' for about a minute or so then it disappears completely.

I'm on a real Mac Pro running 10.9.5.