We had some Arduino Mini Pros around from another project. The seem perfect for listening in on the data that is being sent between the controller and the Quad. Here is the pinout of the Arduino Mini Pro and the way that we wired one of them into the SPI communication bus in the remote control.

(Ignore the red lines)

Notice on Pins 10,11,12 and 13 SS, MOSI, MISO and clock. Since we are using the three-wire configuration we don't need MISO on pin 12.

It turns out that their are several flavors of the SPI bus. The XN297L uses a half-duplex version and only need three wires. 

The wires that we brought out from the remote control PCB are as follows

Purple and yellow is Chip Select

Blue and White(with black strip) is MOSI

Green and Gray are Clock

Here is how we set it up to snoop.

Here is another view for those following along with the home game.

We checked and the Eachine will still pair with the remote and fly.