None of those were build for Raspbian. They were build for Debian and Armbian is generic Debian / Ubuntu.
This method works in local network:
apt-get -y install xrdp vnc4server xorgxrdp
but for the way you want to use it (Teamviewer style) I don't have experiences. Just make sure to use Armbian with a modern 4.19.y kernel to rule out possible kernel related issues.
I can only give you few insights - with a little bigger heatsink and running
stress --cpu 8 --io 4 --vm 2 --vm-bytes 128M --timeout 1000s
I can push the board (CLI) barely up to 80° and heatsink temperature doesn't pass over 50°. In your case, most likely 3D engine (lima) is doing something which contribute to some heating. I would say your heatsink is surely too small for the load, yes, but also this 3D engine is far from fine tuned - its status is "it works somehow". Perhaps Mali DVFS (which is unrelated to CPU speed settings) part is not working properly or not at all. I think that could explain overheating.
For audio - I don't know, but I think I read it sowewhere. Try to do some better searching.
