I'm not familiar with the Graupner radios. Generally speaking, the best way to connect radios is directly via USB. However, I don't know if the Graupner radios can function as a USB joystick, you need to check the manual of the transmitters or contact Graupner for definite info on that. (On some transmitters the USB port is only for firmware updates and such).
The next best ways is to connect either via a USB dongle, or, connecting a regular 3.5mm mono audio cable to the trainer port of the radio and use it along with a software such as Smartpropoplus.
Good luck and let me know if you have more questions.