Please provide more information. How do you have the 5900 connected to the 950? Try using a digital out (Coaxial or Optical) into the 950 and see if you still encounter a problem. Are you sure your speakers are wired correctly, in phase etc.. I have the 5900 connected to the 950 via 6 channel inputs. I bypassed all of the Bass Managment in the 5900 and let the analog 80 hz in the 950 do the work. Mine sounds fantastic with anything I put in it.
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"A smooth sea never made a skillful mariner"