Update:

I cannot believe it!! My rig is still online since my last post and I did nothing else... look at the Screenshot!

https://ibb.co/m20JUH

Absolutely awesome!! 0 stales!!!
The slower card is the gtx 1080 and the first one is always a bit slower when I am connected via Teamviewer or remote desktop.

Hopefully one last question:
Is it possible to run another miner in parallel? I would like to mine with the 1080 another coin, like zcash, komodo or btg.
I tried it with ewbf and only the last card, but it didn't start.
As far as I know, dual mining is still not possible with Phoenix... Or am I wrong?