The throttle is connected to USB controller board inside joystick base with this multiply wires cable with yellow tape on connector, right of Arduino controller (the original gameport cable, I think):
You can fit a DB-15 connector in joystick case to plug/remove throttle if want, in this case reuse the TQS DB-15 connector - is need map the pins with multimeter.
In TQS you need 3 axis - 3 wires
+5V and GND - 2 wires
If TQS gameport cable has 15 internal wires (in some gameport sticks the cable dont have), you have 10 remaining wires to combine in matrix for handle the TQS 14 buttons (if use a HAT in thumb control), e.g a 4x4 matrix (3x5...).
Or, if want fit a mini-stick (PS2 style) in place of the thumb controller in TQS (a pressure device that probable dont work with analog USB controller, and anyway work bad even in brand new TQS):
5 wires for axis (3 TQS, 2 mini-stick)
2 for +5V and GND
10 buttons
So you have 8 wires for combine in matrix for control the buttons. 3x4 = 12 (4x4...)
In this CH Combatstick + CH PRO Throttle (Bu0836), due the need of 20 wires for throttle I use 2 cables between stick and throttle:
http://i62.tinypic.com/i74lyu.jpgOr, if you dont plan play old games of fly in FPS games (BF...) as they have joystick restrictions, ones recognize only 1, fit one controller (MMjoy) inside each controller and avoid this cable mess.