My question now is, will this be resolved with a firewire connection? I.e. should I buy the optional FW16E FireWire Expansion to add functionality of automatically reconnect midi? If yes, I consider so because it will enhance my workflow. (I don't need the audio multi channel funtionality though.)
No, do not get the FW16E if you don't need the "audio multi channel functionality".
To resolve your issue, power on your gear, then power on your computer. Launch your DAW software last. While the DAW launches it surveys what is connected to the computer. It actively checks the computers ports, it
should find all of your connected hardware and establish connections.
By turning off your gear, but not the computer...
"... disconnecting power of all hardware except for the pc." You break the knowledge the computer has of these devices. You need to allow your computer to rescan it ports.
Although you don't mention turning the computer OFF, we are going to assume you let it "sleep" or "hibernate". This action is causing your computer to "forget" what is connected. I'm no Windows expert but if you are saving energy by powering down everything but the computer, instead of just waking the computer - power on the rest of your gear and then
reboot the computer.
Windows will
fully reawaken when you reboot. If not, you will continue to have it baffled by not finding the ports. Avoid SLEEP and HIBERNATE.
Reboot!