Keep it simple!
The stock 3in1 (main motor ESC, tail motor ESC & rate gyro) on the AXE CP (V1 thru V3) is LIPO COMPATABLE!
A 4in1 is a receiver, main motor ESC, tail motor ESC & rate gyro.
This is all you'll need to convert to separates:
1.) A 25amp brushed Electronic Speed Control (ESC) for the stock main brushed motor
2.) A 5 to 8amp brushed ESC for the stock brushed tail motor
3.) A RATE or Heading Hold gyro (Futaba G190 rate gyro, telebee TB-1 HH, GY240 HH, etc.)
On my AXE CPv1 when I swapped out the 3in1, I got a 30amp ESC from Tower for around $40 bucks I think it was a Electri-Fly C-25, the tail ESC was a C-12. The Gyro I had used was a Futaba GY240 Heading Hold, a heading hold gyro holds the tail in whatever spot you want. Where as a RATE gyro requires corrective action depending upon throttle position (this is what the AXE comes with), ever notice with the stock 3in1, when you added throttle quickly that the tail would more right input, this doesn't happen with a properly set-up HH gyro.
If you wish, you could just order another 3in1 it will work fine with a 11.1v 3 cell lipo.