Long storey Rik 🙂
Basically a route used built in navigation i.e. turn left and right to Next way point – a course is just a line you follow 🙂
I just use a course file off road. Many way around it really.
TCX ad GPX are very similar file types – what will ruin your noddle is that the 800 records natively in FIT files 😉
You might want to read this:
Dummies Guide to the Garmin Edge 800
The other thing is to export as GPX and upload to connect.garmin.com and then you can download it as a TCX course file automatically without TCX convertor 🙂