Hi, great simulator/game :)
I just spent a couple of evenings figuring out how to get my FS-i6 radio connected to my Linux Mint 18.2 computer. Figured I could share my procedure.
1) Aquire or DIY a trainer cable to use with the computers microphone input. (I tried a cheap USB audio dongle as well, but the resolution on the input was quite bad!)
2) I found the following branch of ppm2tx to work on my computer after installing some missing packages: https://github.com/rhwilr/txppm
3) Connect controller, turn it on, launch ppm2tx, enjoy!
Before doing this, I already tested Freerider with my Arduino Micro hacked Esky USB controller, and it worked perfect!