All of those are often recommended here, so it's really about your wants and needs.
If budget is the deciding factor you cannot beat the features found in the rz730/830.
If reliability is #1
, well Yamaha is known for that, which is probably why their receivers always seem to be $hundreds more.
If it's about good room correction, features, reliability and power then you can't go wrong with the DM recievers. Throw in there that Marantz is also a good 2 channels avr, so if music is a demand too, then take a look over at AC4L for an amazing deal on the 6013, with 3 yr warranty.
If it's about straight up theater power, sound and room correction under $1500, I think the NAD 758 v3 is often recommended.
I believe I read that an avr will downscale to the lowest level of the connected devices period. Yes I think RCA's are limited to 720x480 resolution.
can chime in and clarify if the DM independent hdmi outputs can play 2 different resolutions.
hope that helped get you started?