I'm fairly certain that Gemini processor would not work in conjuction with your surround receiver/processor in a surround set up. Besides the encoding would not be in the movie sountrac. When watching movies the sound you hear should coincide with the action on the screen. Actually, adding random speakers not accounted for in the soundtrack would most likely have a negative effect. If you wanted all your current speakers on at once see if you have a setting called "stereo surround" or sometimes tagged "party" mode.
Why do you feel you need more speakers, is it room size?
You have 11.1, so do you already have Dolby Atmos? If not, a better, yet possibly, more expensive solution, would be to go to a receiver/processor with Atmos which would give you the over head speakers. Then the Atmos processor would have the encoding to pan the sound/effects correctly to those speakers as well as all your others in the set up. The panning effect and emmersiveness is said to be stunning.
Really depends on what you are trying to achieve, more immersive sound or more speakers playing at once.
That Gemini piece takes a 2-channel signal and manipulates it to some kind of generic surround, looks to be more for DJ application.
