i've bought a cheap 60A PWM Motor driver
Unless its got very well developed skid steer algo, which isnt likely the thing will not steer and have a mind of its own.
Also it better have motor current limiting and motor load compensation capability or it will be hopeless to use, and have inadequate torque or suddenly shoot off like a rocket... Those motors take around 200A at stall. There will be smoke!
You really do need the chairs control system and a high level programmer which is easy. Theres are various ways to make it drivable by RC or by messing around with the bus. Take a look over on the main forum.