Thanks for the fast reply! I followed the instructions in your link (section "DSL modem") and copied:
aca_fw.bin to /lib/firmware/09a9
ppe_fw.bin to /lib/firmware and
xcpe_8D1507_8D0901.bin to /lib/firmware
Afterwards i made a symlink: ln -s xcpe_8D1507_8D0901.bin /lib/firmware/vdsl.bin
Do you have a guide what you did with your 7520 box?
Thanks
Edit:
Playing around with routing (inspired by this post Fritz!Box 7530 and 7490 as Modem+Router combo for 35b Supervectoring - #56 by slh):
I got this:
Looks better. Do you have any suggetions ad routing/interface config for dummies :-)?
Thanks!