I just installed a simple black magic output card on a 2008 Mac. The output card doesn't have audio output.
Video out from the card works great, but the audio will not output (obviously because there are no audio outputs from my card), so I want to activate the internal speakers for this. How can I do that?
If the card you have only has HDMI and SDI, then audio is going out to the card, and then to the monitor. So you either need to tap audio from the monitor, or get an HDMI or SDI splitter (whichever one you are NOT using) to then send audio to the mixer. As Michael said, you can't have audio come out of a separate place than video. If an IO is connected, then audio goes to it, period.