The SL 16R and the SL 64S are unique in the Series III range of mixers. They use a modified USB and AVB routing. All other mixers (!) are 32 channel mixers which share their I/O and routing configuration. You can delete channels/tracks you don't need, when you use a SL 24 or SL 24R. The SL 32SX has the same physical inputs and outputs as the SL 32, SL 32S and SL 64S.