There should be a dedicated network for the communication between your devices. You need a router supplying dynamic IP addresses for this network. It may be that you have to configure your devices first, if they have been tweaked (if you bought them new they are set to dynamic addresses). This router has to be connected directly to your mixer, which means that the mixer does not need a dongle, but the CS18AI. Your PC should be able to join the network. If your PC has FireWire you should get the direct connection between mixer and PC running first and only after that think about networking.

There are several threads here dealing with this theme, so feel free have a look around... For AVB functionaliy you need an AVB switch. There is one coming PreSonus "soon".