Ive got the 50ex700b, and I did have a sony str-dn1040, where I had the same issue. I connected my ultra hd bluray player direct to the tv and used the second hdmi on the player to connect to the Amp.
However, the more 4k devices you add it starts to be a problem. I did add a new Tivo and used a hdr switch to switch between the Tivo and Bluray player, for audio from the Tivo, you could use the ARC or optical out from the TV. However this just created more issues, I had no end of issues with ARC, mainly cutting out when using the on board apps and the CEC didn't play nicely with the Amp either. I ended up buying the sony str-dn1080 which supports hdcp 2.2 and is fully compliant with 4k. So that solved one issue and I can now output to a second zone without any problems.
Although I am still plagued with CEC/ARC issues. So I have disabled CEC on the Amp and use optical for the onboard Apps for 5.1 audio and handle the control with my harmony ultimate. Granted I lose the option to control volume with the TV remote and no dolby digital + audio from netflix, but for my sanity I went with this config. There are still issues with audio when using netflix, the only solution is to power the amp and tv off and then power back on (making sure the amp comes on first). I really like the TV, but still debating whether to return it of not as the software and smart tv functions are unreliable compared to my previous Samsung TV.