I am not sure and I tried to search but the setting says 'if you need more bass from the subwoofer' but I will play with it some more.Isn't the double bass setting something that uses your L&R mains to also produce bass?
This generally is a setting that is frowned upon, if I'm recalling correctly.
**Edit - I found some posts and it does sound like this uses the mains and sub for bass. I will turn off and muddle some more.
Crossover is set to 80hz still
MCACC set my L&R Mains and my center as large.....but I cannot, no matter what I do (Attenuation Channel A 100%) get my receiver to drop the subs to anything lower than 0. The very first time I ran it set -0.5 and attenuation was around 60% so not sure what as the subs are much louder at 100% but my receiver just goes to 0 now.