80 Hz is a typical crossovers setting for pairing monitors with subwoofers for a reason. 
Also, keep in mind that you are augmenting the bass response from your monitors, not supplanting it with most integration set ups. Chances are, you were starving the subwoofer, in terms of its normal range, when you set the crossover so low the first time.
A great subwoofer will have an impact on a much wider frequency response than one would instinctively think. Start with the manufacturer’s recommendations for crossover settings and then tweak the settings from there. I have found that to be the most successful approach, generally.
Conventional wisdom favors corner placement for subwoofers. For what its worth, in my rooms, I have never favored corner placement. You might consider moving your sub out of the corner and out further into the room if it is currently more or less in the corner. Chances are you could smooth things out a bit more.
Anyway, glad to hear you got things dialed in and are enjoying the set up.
Cheers.