Comment 2 for bug 1451334

I think the problem is a bit more complicated and specifications should be more discussed.

There is not only the ChannelX groups/sections. What about [master] and [playlist] controls that can be present on the two controllers ? (may also apply to effects, microphone, samplers, etc..., I don't know exactly by now what is the exact list of sections)

Probably crossfader can not be activated on the two controllers at the same time or you will always have on of the crossfader not in sync with the other and Mixxx interface. should we deactivate the [master] section of one controller ? so we need to be able to chose in preferences the controller on which the [master] will be deactivated.

On the other hand, It could lead to additionnal buttons/knobs/whatever that are redundant between two controller and you can use for other controls. Why not let the controller xml files define a primary (when master) and a secondary command for each button ?

In this cases, we need to :
- have a way for xml files to say how many channel they use
- let user assign each channel to a controller channel (which controller and which channel of that controller)
- let user choose which controller hold master, playlist, etc... sections/groups
- have a way in xml file to define the buttons primary assignation for master, etc... sections and other assignation if the controller doesn't have the "master", ... function

this way, you can imagine using four 1-channel controllers (one for each deck) and a "master" controller for mixing and common commands (but it seems to be an expensive setup).