I’ve asked this twice before and it’s gotten lost in the shuffle, but now that I actually have the thing it’s become more pressing. Can someone tell me whether it’s possible to mux the 5.1 into the existing BD with the seamless branching using some manner of freeware, or am I going to need to make an MKV?
Making an MKV would be the easiest option. But yes you could mux it with TSmuxer so long as you split the file first into the two parts first (flyover and main movie).