Despite having my room heavily treated, and setup by someone who does it for a living, I still have a +6-9db bump between 125->300hz. The guy said it would take room re-construction to correct and it is not something I can currently do.
He did suggest trying ARC and I did. I never had a problem with ARC 1 or II crashing my system but the results can sometimes be frustrating.
I can listen to reference material and it sounds ok until I turn ARC II on and then it sounds great. It's not as muddy and the clarity just jumps out. When I mix with ARC II on the master buss everything is clear and no mud. When I export, with ARC II off, and then listen to the mix on AKG240s headphones everything is bass heavy. Of course if I listen to it on the monitors with ARC II off it is muddy but to be expected as it is the room I am listening in.
Seems like damned if you do or damned if you don't. I guess it just comes back to what Bit said about learning your room/monitors whether you choose to use ARC or not, you will still need to correct for room/monitor issues in your mix...