The bottom line is that the benefits you're describing are easily outweighed by the risks. And the "manufacturers of consumer electronics" you've named are not the typical Japanese or US A/V companies making receivers/pre-pros. This is why none of them allow (let alone encourage) hacking of surround processing or signal routing in their products. And those are the type of products and functionality we've been discussing. Likewise why companies like Dolby and DTS are not accomodating hackers in their processing/decoding technologies.

As I said earlier, I'm all for added options (at least ones that are useful and makes sense). But the functionality you're wanting would require an actual mixer, which I still think is your best bet if you want to re-mix soundtracks the way you've described. There's nothing wrong with what you want to do, it's just that a home theatre surround processor is simply the wrong tool for the job.