Been lurking and reading ,and thought I would share with all.
1) Just got a new MRX720 last week. What a great receiver. I had an older Arcam AVR350, which was great in its time, but the difference between that and the MRX720 is night and day, the 720 sounds so much better (with ARC) overall in my room even without Atmos and/or lossless codecs, which of course I now have and didn't have before either adding to the sonic improvements even further, by a lot. I bought the MRX 720 in part after doing my "homework" on avsforum, just like I did to buy my original equipment (the receiver and Paradigm Studio 60's, CC690 and ADP 570's along with a Hsu VTF-3 sub). In a mid-sized room like mine, there is no problem driving these speakers with the MRX 720 without an external amp; I will connect some in-ceiling speakers soon but don't anticipate any issues driving those two (5.1.2 set-up due to my room limitations) from the MRX-720 either. I suspect that the new Arcam 390 with Dirac is good as well but honestly I can't imagine that it can be very much better if at all than the MRX 720, and even though there is concern about the power specs on the MRX 720, the Arcam is speced to be even lower power both in 2-channel mode and with all 7 channels driven; in my room and system, the Anthem has tons of headroom to spare and is doing just great; no need for an external amp whatsoever from what I can tell.
2) I had an HDMI handshake issue appear but strangely after uploading ARC and only on one HDMI input/connection. I did all of the usual debugging stuff and finally remembered that in my experience the only way to solve it for me on other equipment, which worked in this case as well, was to disconnect all of the cables, including importantly the HDMI out cable, then AC power off and AC reset everything, including the MRX720 as in the manual, then plug the cables back in, and then power everything up again. I had to do all of those steps in that order; leaving one out, like especially leaving the HDMI out cable connected to the MRX720, even if the display/TV/panel was powered down/off, didn't do the trick for me. Now I have a rock-solid signal with no glitches in any way from all of my HDMI inputs (admittedly no 4K yet but nonetheless is still fine), so maybe that will be of help to others who are having issues. My next step was to do a factory reset but there was no need, it wasn't a firmware issue it was an HDMI key and handshake issue that was somehow introduced into that connection when I uploaded ARC (I think) but regardless it is now gone.
My only other non-routine issues were in the network connection; turns out that you can not have the ethernet hard-wire connection plugged into the back and try to establish a wireless connection to the MRX; it is one or the other exclusively, and Anthem helped me end that frustration; still could not establish a DCHP IP address for some reason though but a fixed IP address did work and is holding solid; strange but can live with it.
My Oppo BDP-83 works fine with the Anthem so no problems there.
Also my Harmony 900 remote controls the Anthem MRX 720 perfectly as well; the only minor glitch for me was that for some reason the set-up didn't properly populate the activities with the proper volume control keys to control the Anthem even though I told the Logitech program that is what I wanted to do; that was fixed quickly by individually going into each activity and assigning those hard buttons to the Anthem volume up and down commands, and it all works fine. Did not have to train the Harmony to learn any commands, all of the ones in the Logitech database seem to work just fine for the MRX 720 as far as I know now.
There is one interesting/minor thing that maybe someone here can comment on (in view of the above)
After running ARC, it set all of my speaker levels as follows: FL: +6dB, C: +4 dB; FR: +6 dB; SR: +9dB; SL: +4 dB; Sub: +6 dB.
I only assume that it did that in order to get them all to some standard SPL level at the reference 0 dB volume setting on the receiver; otherwise I could have subtracted 4 dB from all of them and ended up with the same relative offset levels. Should I be worried at all about clipping and override these levels and subtract 4 dB from all of the values, or just leave it where it is now (my default action is no action).
Also have not messed with the "room gain" setting in ARC; do people really recommend increasing it (ARC set it at +3.25 dB for my room) and if so to what value?
Thanks lots for all of the help and hope that the above info is helpful to others as well.