This is with the output expander right? If so, the Pixelblaze output type should be set to Output Expander. Then you can add a board config using “add board” button, then configure the expander channels as needed.
No need to make extra connections, those are connected internally and you can use either.
Remember don’t connect USB and external power at the same time! How do you have it connected and powered?
Can you get a screen capture of your settings screen?