The guy really didn't knew what he had, he asked 175 euros, but as he only had it advertised on tweakers.net, he didn't find any buyers.
So he said I could have it for 50 euros. He REALLY didn't knew the system, good for me (or he just thought it was broken, as is was it the slave setting). One time luck, as he only had one.
I expected a lot of scsi problems, as the origin only has place for 2 cdrom's and I only placed one. Looking in the case, I didn't find 6 other drives
so it's indeed wrong.
But I installed irix without a cd problem, so it works fine.