Mahlzeit,
You can use two Efficientnetworks Speedstream 5851 in back-to-back configuration. This means that you have to configure one device as CPE and one in CO-Mode (Center Office - it works like a dslam then). I have done this already twice for projects over here. You will find what you need at http://kb.efficient.com/ if you encounter any problems, i got a working setup over here and can have a look at my configurations if needed.
cheers, Michael