Do you get sound out of the headphones plugged into the Wego? That’ll tell you if there’s a problem with the sound card in the controller.
And do you have anything else you can try plugging into the speakers to test them?
Try and isolate exactly where the problem is: laptop / controller output / speakers and that’ll make your fault finding easier!
And you have updated your version of Serato right? I think the newer versions play nicely with El Capitan now, but older versions did NOT. I’m still holding off on the upgrade myself 🙂