Need help on PID Tuning / Big X8

I’ve just finished my X8 build and flew it the first time yesterday.
While hovering I got slow oscillations which look like my Roll/Pitch P is too low. On any control input I get overshooting which nearly leads to a crash.
I also tried autotuning but that wasn’t successfull either, as you can see on the Video.

My config:
Motors: Sunnysky x4108s 380kv
ESC: Hobbywing X-Rotor 40A
FC: Pixhawk with APM:Copter 3.3 RC1 (Tried 3.2.1 before but with the same problem)
GPS/Mag: Drotek M8N
Battery: 2x 5000mah 4S 20C

Flightlog: [attachment=0]2015-04-18 19-27-10.log[/attachment]
Video of the flight:

Can you give me some advice on tuning it so I can at least run AutoTuning?

Thank you!

Did you ever find anything that helped with this?
I was trying to tune my 3DR X8 and it had very similar oscillations. I’m using AC3.3.3.