This is just a guess but,

When the DS2416 is combined with an AX44, channels 13 - 16 share the AX44 inputs 1-4 with software outputs 7(L/R) & 8(L/R). The default state of the DS2416 is to have the outputs selected. The inputs have to be selected via the software - in your case Logic. I haven't used Logic so I can't tell you how to change the settings in that software, but this is the first thing I would check.