In this case you would simply create sub mixes in Aux and work it that way around. Review the video posted along with this digital AVB sends to get a better understanding.
AVB Sends 1-8 = Channels 1-8
AVB Sends 9-16 = Channels 9-16
AVB Sends 17-24 = Channels 17-24
AVB Sends 25-32 = Channels 25-32
AVB Sends 33-40 = Aux input 1L, 2R, 3L, 4R, Tape In L, Tape In R, Main L, Main R
AVB Sends 41-48 = Mix 1 through to 8
AVB Sends 49-56 = Mix 9 through to 16