For the final two mixes, change a Group on the mixer into a Mix, then route that mix into a matrix out.
and YES, you can control these final two Group mixes via QU4you app.
(if you haven’t already purchased, I greatly prefer Me-1 over Me-500, because the Me-500 forces you into carefully selecting which sound sources are in outputs 1-16 in the I/O section.)
D-snake just gives you another location for your aux outputs. It doesn’t add auxes or change mono to stereo. I happen to like my Ar2412 being permanently wired to IEM transmitters, but that is a matter of convenience, not necessity.