I was looking for a solution to have a night mode on my stereo hifi system when looking a movie on my projector, but never seen something like this. But the dac+dsp sound like something that could do that. So I try it
I have done this maybe two years ago. prepare something to share last year and only share it now...
It's not perfect but I do not have to play permanently with the remote when I'm watching a movie, sound is compressed so I heard the voices and FX are not too loud.
So if someone have this problematic, you can see this project on GitHub, all is shared : all the files for the raspberry, for the DSP, for the iPhone app (not for android now) and for 3D printing the case