Dxtory does not only come with a demuxer it also comes with a mixer (to mix all audiostreams to 1 audiostream). But either way... it's additional work that has to be done by the user and when processing many files it is a hassle when it shouldn't be any problem at all.
Either Dxtory should be able to mix all audiosources to one track by default - while recording - like all other game recording programs offer; or Premiere Pro should finally import just everything that's in the videofile. The latter would be my prefered solution.
I mean an AVI file with 2 audiostreams (e.g. 2 audio languages) is nothing alien and nothing new... just like a MKV with more than 1 audiostream... which Premiere Pro CS6 ignores completely (MKV that is).
edit: I'm aware that this is an older thread but as I found it via google I assume other would find it too when searching for an easy solution to import an AVI with multiple audiotracks.
Message was edited by: Mopsi Leet