The answer to that question is more complicated than it sounds, because DEQ adds bass to more than just the subwoofers. And, the amount of bass that it adds to the subwoofers is variable, ranging from about +1.1db at 70Hz, and above, to +2.2db at 30Hz and below, for every -5 MV from Reference. So, at -5 MV, DEQ is adding about 3.3db to all of the channels, and a variable amount to the subwoofers, increasing to approximately +6.6db at 30Hz and below. But, of course, there isn't always content below 30Hz--especially with most music and many TV shows.
As stated in my earlier post, at your typical listening level, I would start by adding about 5 or 6db of subwoofer boost, and I might also experiment with adding a few decibels of bass boost to the two front speakers, with the tone control, once you turn off DEQ. But, ultimately, your own preferences need to dictate what you do, and those preferences may change slightly depending on the listening material, including how much deep bass it has. I think that most people would probably add much more bass boost for 5.1 movies, than they would for music.
I would seriously recommend reading the article on DEQ, to understand more about how it works and what it is doing. That will help you to better understand what you are hearing, and also to better understand methods that you might like to use to change what you are hearing. This is a direct link to the section on DEQ: