Hi Kai,
I'll try to explain the two possible connections of additional servos:
1. Servos over the X2 servo outputs.....it should be no problem. There must be just one ESC/BEC power supply over the Servo BUS!!! One can connect 7 servos + ESC/BEC to power the servo bus as it is not powered by the Power Brick;
2. If one needs to connect additional servos to the receiver, this is a different beer...
. The X2 has a superb protection for this - a Schottky forwarded diode + a 200mA resettable fuse. These two components prevent from back EMF and from overloading. So if one needs to connect additional servos to the receiver - no problem, just DON'T power the receiver from the X2, but from an external ESC/BEC which is used to power the additional servos connected to the receiver. That's all.
Best regards
Nick
P.S. ...each servo connector has its own 100nF MLCC for spike suppression.