jack audio multiple outputs

It would be really useful it it'd be possible to have multiple audio outputs when using jack (one by instrument).

Main use-case is: I've done a composition within musescore which I'm happy with and now, I want to mix it externally (e.g. with ardour).

For information, I know that Hydrogen is giving this possibility when you go in the Preferences -> Audio System tab -> "[] create per-instruments outputs" for information.

lasconic told me on IRC that it wouldn't be that easy given the current code implementation, but ... hey ... impossible n'est pas français :P

Hope this feature can reach MuseScore which would be really usefull for people using MS in an advanced scenario.

BTW, you guys are doing an amazing work with MS, kudos to you all involved in !