Yes, you’ve got it right. Channels 3 and 4 are the ones to use when connecting your CDJs to the XDJ-XZ. Plug them into the line inputs (not phono), then connect all units via Ethernet link so Rekordbox can recognize them as four players. Just make sure your laptop and all devices are on the same network. Once linked, you’ll see all four decks show up in Rekordbox’s performance mode. It’s a smooth setup once configured, though it can feel finicky, kind of like scheduling with amazon flex, everything has to sync perfectly or nothing works!