Yes exactly. You can daisy chain them using the in/thru sockets (with each needing its own power supply) or feed them an individual cat 5 cable from the P16D splitter - which I think means they don't need separate power.
Either way, each unit gets 16 channels from the XR18 that can be mixed, panned, eq'd etc completely independently of each other and independently of every other P16M. In stereo.