If you go with the 975 you can also get the TE HDS-42 which will split the 4K video to your TV and send the HDMI audio to the 975. So you can get all HDMI connects with the 975 and not mess with optical.

The 976 gives you the added benefits of XLR outputs and PEQ along with the Bluetooth. If these are important to you then go with the 976.

I've been happy with my 975, though the PEQ of the 976 is intriguing.