There is a number of PCIe cards based on NEC/Renesas chipset available at Amazon Germany. Here is a couple of examples:
http://www.amazon.de/4-Port-Express-Schnittstellenkarte-Controller-spezifiziertes/dp/B00AFC5W92/ref=sr_1_2?ie=UTF8&qid=1388353078&sr=8-2&keywords=usb+3.0+pcie
http://www.amazon.de/Transcend-Schnittstellenkarte-Adapter-PCIe-Ports/dp/B003MVJG8Q/ref=sr_1_5?ie=UTF8&qid=1388353078&sr=8-5&keywords=usb+3.0+pcie
http://www.amazon.de/Hama-USB-3-0-Controller-PCIe/dp/B0038G3VJ0/ref=sr_1_34?ie=UTF8&qid=1388353856&sr=8-34&keywords=usb+3.0+pcie
http://www.amazon.de/LogiLink-PCI-Express-Schnittstellenkarte-f%C3%BCr-Ports/dp/B00339X1PQ/ref=sr_1_40?ie=UTF8&qid=1388353856&sr=8-40&keywords=usb+3.0+pcie

Thanks, I just bought one of them. I hope that that's my last try, this kinda annoys me currently. Not because it's not working, but because I really don't know what to do about it.
I'll tell you if it works in a few days.
Anyways, thanks for your help and wish me luck :D

Sure I wish. Have nice holidays :)

Thanks. Actually, they worked out pretty well, because the new usb controller works perfectly. I can now connect two kinects without any problems.

I get an average angle error of about 6 degrees with the 180 degree setup. Is that too much or merely normal?