Audio start delay not 100% gone
I picked up a MRX710 a few days ago. Running the ARC was very easy, even using a Macbook and Parallels. I was dreading that, but I had no problems at all (other than having to connect a CD drive to get to the calibration file). My receiver doesn't have any brightness difference between medium and maximum on the front panel display, but that hardly seems to merit an exchange, especially since this unit is eventually going to live in a closet.
One observation is that the complaint that a lot of people mentioned early on - the audio delay when changing music tracks on an optical/coax source - does still seem to exist, but it's very slight. I'm running the most recent firmware (1.2.1), with a Mac connected via coax, and I've noticed that if I pause playback for 5 seconds or so, and I resume at a new track, the first attack on that track is clipped. This seems to be much less severe than people originally reported - it's literally just the attack, just milliseconds - but it's still there. I don't understand why that firmware change couldn't completely fix this, particularly - as many have mentioned - the Japanese receivers don't do this. (I've just switched from a Denon.) The problem is unique to the coax (and maybe optical) digital connections, but doesn't exist via HDMI, presumably because that signal is constant.
Anyway, that issue is still there, unless there's some hidden newer firmware I don't know about. Great receiver once the audio is playing, though.