Thanks a lot, should have edited my post, I also just figured out My OSMC is pretty useful 
A Transmission:
Add a “NICE” level to the systemd service unit. For example, I am using:
Nice=10 for Transmission. Nice=7 for Syncthing.
Kodi of course should have a higher nice level (-5?).
XBian uses a dynamic way of changing nice levels, not sure if that is really necessary.
Closed as in App Store