OK, I’ve tried to use the same retailer’s website just for consistency of information:
https://www.crutchfield.com/S-baFGbkAOimX/p_305UBDM85K/Samsung-UBD-M8500.html
https://www.crutchfield.com/S-8fTYSqGti92/p_022RXV379/Yamaha-RX-V379.html
https://www.crutchfield.com/S-OBiWN7gEaS5/p_30555M6300/Samsung-UN55MU6300.html
As you said the player has a single HDMI 2.0a, supporting HDCP 2.2 as described in this link, while the reciever has 4 x HDMI 2.0 connectors, also supporting HDCP 2.2 according to this link. Even Yamaha’s Press Rlease says it does HDCP 2.2:
https://usa.yamaha.com/news_events/2015/20150428_yamaha_rx-v379_av_receiver_places_4k_us.html
TV has 3 x HDMI 2.0a, supporting HDCP 2.2, so from these specs your entire video chain is HDCP 2.2 compliant, and shouldn’t need to convert to HDCP 1.4??
A bit more digging brought up this article:
http://4k.com/news/how-hdmi-2-0-helped-4k-advance-8437/
IMO, it appears the issue is the reciever is only HDMI 2.0 not 2.0a and so it’s not an issue of HDCP which is the problem, but the HDMI specification. Hopefully someone will chip in if I’ve got this completely wrong. If it were HDCP ‘standards’ as an issue, I can see how a box like you suggested would work, as it legally decodes 2.2 protection, and then re-protects at 1.4 which is supported by more devices. I think your issue is that the signal coming out of your player is then having the additional commands in the 2.0a subset ‘stripped’ which are then required by the TV set.
If you’re still covered, I would look to exchange the Samsung 8500 for the 9500 which has the dual HDMI connectors.
HTH