Over the past 12 yrs I've owned the following pre/pros like: Sherwood P965(SNAP), Rotel RSP-1066(no room correction), and Marantz AV7005(Audyssey MultEQ XT), and receivers like the Denon AVR3300(no room correction), Pioneer Elite VSX-92TXH(MCACC) and now Anthem MRX300(ARC).
ARC is a bit different than Audyssey, MCACC ,YPAO etc... because you load the ARC software on your laptop and connect the mic to the laptop or PC and then the laptop is connected to the receiver. While the others use the receiver to do all the measurements ARC's uses your laptop to do all the measurements and then after you are satisfied with your graphs you upload the result to the receiver. You can also make changes to the results as many times as you like and see the results in the graphs on your laptop and then just upload them without running the measurements again. Of all the ones I've owned the Sherwood P965 and the Anthem MRX300 are the best sounding units I've used as a pre/pro in my room with my amps and speakers.
To my ears ARC is the most impressive room correction I've heard in my room with my gear. After having ARC I can't see myself buying anything again without it. I didn't know much about ARC before buying the MRX300, because it was previously only offered in Anthem's expensive pre/pros, so I just never read about it because it was in units out of my price range, but now I'm completely sold on it.
"What do you mean it's too loud? My ears aren't even bleeding yet!"