FIRST, report the lockup to Anthem and request 50.12.
As for your Center being set to 120 and your surrounds being set to 100, based on how your speakers measured, they look to be exactly correct. Your speakers simply don't go any lower so picking a lower cutoff will not help.
Now is it an issue that your cutoff on the center is 120 (and for that matter your surrounds at 100)... yes, this could be a bit of an issue as your sub is currently at 80. This leaves a big gap between between 80-120 where your levels will be to low for the center channel.
In all likelihood, there is nothing that is going to improve your center or surrounds that will get them to go lower... so the place to focus is your sub.
Your sub looks quite capable up to 120Hz, it simply needs some repositioning to get it there naturally. Use Quick Measure to play with your subs position and see if you can get the dip at 60 to come up some and perhaps the peak at 40 to come down some.
If you truely cannot move your sub, it maybe possible to tell ARC to use 120 on the sub and it may be able to mostly fill what is missing. THIS IS NOT THE RECOMMENDED APPROACH! And for most people just changing the cutoff would likely do very little. However, in your case it may work, you would need to try it. If you do, please post up your graphs so we can see what they look like after you change your sub from 80 to 120 and recalculate.
Lastly, what did ARC set your Speaker Calibration Levels at? I think we should check that your subs levels are correctly set and that should tell us.