I absolutely love ARC. It's made mixing so much easier, especially below 300hz. The amount of clarity I can hear in my old Mackie HR824's (which are known to have a sorta flubby low-end) blows my mind.
A recommendation, get winamp if you don't already have it, and the vst host for it here
http://www.savioursofsoul.de/Christian/programs/winamp/ With that you can listen to music/masters/mixdowns, and still still get the room correction going on.
Arc has helped my mix translate to other systems so much that I rarely even need to check them in other systems. A lovely piece of software.
Mark