Denon avr-3806 Bi-amping issue

Hi there music lovers,

My problem is this:
Speakers are bi-amped on my Denon avr-3806 and want to boost the low section.
The Back Surr. out drives the lows on speakers and yes, power assign has been set at "front".
I've searched the board for almost 3 days, but cannot find a thing to this problem.
I know this is possible but don't know how anymore.(I've done a complete reset on the amp).

Thanx

Come on guys,

To all denon avr 3806 / 4306 owners.
Need some help with it.

Greetings.