You write that your outputs 11-12 are matrix outputs and you have certainly set them up that way on your console – right?
Matrix outputs are also used to output a mix of the inputs (via groups/aux/main).
And that is probably what Tobi meant.
But now it sounds like you may not have created such a mix at all – perhaps all the faders that could be involved are closed.
In that case you should check again whether 11-12 are actually patched as matrix outputs, or perhaps completely differently, e.g. as dir outs, which could possibly explain your problem.