I don't know of any 5.1 wireless optical audio options.
The only way to get the best audio quality from the BD player is HDMI directly to the receiver. I would suggest you move the receiver to the back with the other gear. Now you have short cables for sources and the projector. Much cheaper and better than wireless HDMI. You can run speaker wire to the front and either use interconnect or wireless for the sub. I am not a fan of putting the only sub in the rear but if you do that a short interconnect will work.
Get a Logitech Harmony Hub and remote to operate the entire system. They have an app that works with it too, You could even add an Alexa Dot and do voice control through the Harmony Hub. Pretty cool.
If you go for 4k the new JVC...