Just checking in, thought I'd throw out another option before you start lifting carpet and getting yourself into trouble.
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One way to get picture and audio to the Dining Room without having to run new cables is to change the connections just a bit. So, set HDMI OUT to OUT 1+2. Video will be output to both TVs. Then, rewire the speakers from the Dining Room. Move them from the SURROUND BACK/HDZONE speaker terminals to the FRONT HEIGHT/WIDE
B terminals. Go into the speaker configuration and set it to
7.2 channel surround system & Speaker B connection. Set the SURROUND BACK/HDZONE speakers to none if you can do so. This will turn off the SURROUND BACK/HDZONE amps when not using
Speaker B. So, with these settings, no more Zone 2 or HDZONE settings applied. This new configuration will get you a Main Zone with two monitors, HDMI Out 1-Living room and HDMI OUT 2-Dining room, and A-Living Room and B-Dining Room Speakers. So, lets say somebody wants to watch something using a Smart app on the TV in the Living Room. They can do so and use the TV speakers. At the same time, somebody can go into the Dining Room and watch something from the cable box that is connected to the Pioneer. Setting the speaker output to
B on the Pioneer will turn off the speakers in the Living room as well as both Subs and just the two speakers in the Dining Room will be on.
I'm assuming both TVs and the Pioneer are connected to the network. If not, get them all connected asap. Also, some cable providers have an app within Samsung's Smart TV App Store and can be downloaded and used in place of a cable box. With the Pioneer connected to the network, you can download the iControlAV5 app for iOS and Android devices to control the Pioneer from the app. It also supports web setup so adjustments to the system can be made from a PC or tablet.
Like any system, there are limitations. With the newly proposed setup, one could do the reverse and have the speakers on in the Living Room but because there is a Sub in the Dining room, somebody using the smart apps and TV speakers in the Dining room would also have to physically turn off the AV Link Sub as it would be playing the signal from the Living Room. Your setup makes a good argument for the need for Zone 2/B Speaker assignable Subwoofer Pre Outs. Also, this setup limits video output from the Pioneer to the same source for both TV's. The use of ARC is only available from the HDMI OUT 1 port of the Pioneer so it can only be used with a TV connected to that port. Viewing different sources with different zone speakers for each room would require the rewiring for the Zone 2 & HDZONE setup.