Manfred, awesome setup! I would try setting your subwoofer to 80Hz and go from there. In a two channel setup this is the hardest part of getting your sub to blend well with your system. I would us DIRECT mode on your receiver if it allows you to do so it might turn off your subs that way it bypasses the filters in the system. If you really want to get creative you could download REW and install it on your computer. I then would get a UMIK-34 from Dayton Audio on Amazon and run a subwoofer test sweep. Find out if you have nulls in the bass and them add distance so it could flatten it out. Hope this helps, Happy listening.