A 2.4GHz receiver.
I do not know the protocol of the G6 transmitter, but most likely Bluetooth since the app works on any Android phone. But there is no user pairing involved and I have nearly zero experience with Bluetooth on Arduino.
I would love to get the transmitter data using only Arduino boards. It would keep me in familiar territory and I wouldn't have to buy the relatively expensive Wixel boards. If it's possible using the ArduinoBT or HC05, I would be quite happy.
Admittedly, I haven't examined the code for the Wixel app to see how it connects to the transmitter. But it's written in C so rewriting it for Arduino C++ shouldn't be a terrible challenge.