[nickr]

I am not sure, but you can run a script at every startup in /storage/.config/autostart.sh

[kimkl]

Well glad to hear m8, if your happy with it then lets leave it at that, and not go into, that you still only have 2.1 even after changing channels, to 6ch, if you happy with it i am to

Okay i can't let it slide just in case someone tries to "wire" their speakers according to your image,
In short first you are probably, hearing sound from all speakers, but that is because you have "tricked" the system.
How? by using LFE, What is LFE:
LFE stands for low frequency effects, look it up,
So how did you trick the system: if there is no subwoofer speaker present then the bass management system can direct the LFE channel to one or more of the main speakers.

Last Note never never never connect any system, in the way the image shows, look it up why.
In order not to get nickr, blood temp rising i will end here, i just wanted to give a heads up to anyone thinking you can wire your system like in the image, you can but, you will not like the outcome, for "tricking" Kodi to play 5.1 go crazy.

So everything was within topic so ill end my reply here
Thank You