I understand the AX2550 can control a maximum of two servos in position mode; which in my case would control the brake and steering. The engine I'm working with has electronic signals perfect for drive-by-wire for the accelerator and transmission - could those be controlled easily with the standard AX2550 as well? Or would these need to be controlled outside of your product?
The AX2550 has one output (Output C) which can be activated by radio or RS232 command or Via Input E; it could be used for one of the two inputs you require.
The other input would have to be driven externally.