Hi,
I've been looking for this for a long time, and spent many hours in the last few days looking for a solution, but could find nothing.
I love watching DVDs and other media files with friends. I prefer watching the original soundtrack (usually english) while many of my friends prefer the german (or spanish) synchronization.
I would love to be able to output both at the same time, the original via my main soundcard (MacBook digital optical out, with 5.1 where available), and a second language (such as german) via a USB-Soundcard to headphones, or directly to Bluetooth-headphones.
If someone develops this feature, please contact me - I'll have a crate of beer delivered to you, or something like that!
thefool