FWIW
I have an Oppo 205 but use it HDMI to a AVR. With the AVR set to neo back I get sound from all 7 speakers even with 5.1 content.
I believe if go to the Oppo 205 menu, then go to the Audio Output Processing and select Speakers, it will give you a menu that has a downmix option. My guess if you select the 7.1 option you would get sound out of all 7 speakers regardless of the input format, but I've never tried it. Please let us know what you find out.
Also, I use my better speakers at the sides, but mostly because they are floor standers and didn't fit my room at the rear.
I have an Oppo 205 but use it HDMI to a AVR. With the AVR set to neo back I get sound from all 7 speakers even with 5.1 content.
I believe if go to the Oppo 205 menu, then go to the Audio Output Processing and select Speakers, it will give you a menu that has a downmix option. My guess if you select the 7.1 option you would get sound out of all 7 speakers regardless of the input format, but I've never tried it. Please let us know what you find out.
Also, I use my better speakers at the sides, but mostly because they are floor standers and didn't fit my room at the rear.