Ah no there is not such an option on the AVR, I was thinking maybe there is some hardware or even software for this. Cause I got the front 2 speakers to work now, but the center, 2 speakers in the back and subwoofer don't work at all now.
But all in all I think I'll just try the converter first and otherwise I'll keep watching on some second-hand only shops to see if someone will sell an useable avr. Cause I don't think there will be any new avr's that cost ~100,- euros right, they all seem to be 500+ eurps, or am I just looking at the wrong sites.