I have to guess a little, because I don't own a NSB stagebox, just SL 16 and 32R and 16R. Your NSB stagebox is probably delivering inputs 1 to 16 to your mixer. This happens via AVB and (I guess) you have to set the input source of the mixer's channels to "Network" to receive and process the signal. You have that running, as you say.
Studio One and Capture receive their signal via USB from the mixer they are connected to and by default (all routing resetted), AVB and USB are set identically for inputs and outputs. This simply means that a signal coming in via AVB 1 input is automatically routed to USB input and output 1, which is the default also for Studio One if you load your mixer's template when creating a new song. The signal "chain" is AVB 1 -> USB 1 -> track 1.
Try to make your connections based on these "network presets". PreSonus has invented these presets to make reacording and networking easy. Nevertheless things can become complicated very fast, but the basic "factory" settings should get always you going.
