I may not have been fully explanatory in my previous response.
So the Denon does have a subwoofer output - but all that is doing is making a 'copy' of the left and right signals, and then summing the left and right together. It MAY have a low pass filter involved. A low pass filter is a filter that attenuates the sound above a certain frequency, so you would stop the high frequencies from even getting to the subwoofer. A subwoofer with a crossover knob does this also. But the main speakers still get everything, which can make good integration somewhat more of a chore. Think of the subwoofer as supplementing the main speakers in this scenario.
What bass management does is you can set a low pass filter for the sub output, and a separate high pass filter for the main speakers, so you prevent the highs from going to the sub, and the lows from going to the main speaker. This is more like what is happening in the main speaker between, say, the midrange and tweeter. The signal gets split and aligned so that they smoothly roll into each other. It's like adding an extra set of bass drivers to your main speaker, rather than being a separate thing. It tends to be much easier to integrate, and can help improve the midrange performance of the main speakers because they don't have to deal with the low stuff.
As I say, it's a nice to have.