How to switch sound output between optical and inbult speaker?

[88 King]

I have a digital-to-analog converter connected to the imac using the 3.5 mm headphone/optical output. However, I can't switch output between optical and inbuilt speaker. The only way is to unplug the optical cable. I've attached a screen shot of the sound Settings

Does anyone know how to switch between optical output and inbuilt speaker?

The DAC can accept USB input, but all the USB ports are occupied at the moment.

Thanks

 

[alust2013]

I'm pretty sure you just have to unplug it. It's like putting in a pair of headphones.

 

[John T]

There is an inbuilt switch incorporated in the headphone socket that switches the internal speakers out of circuit when headphones (or anything else with a 3.5m jack plug) is plugged in.

If you want to use the DAC and listen via the internal speakers, you'll have to plug it into the USB socket.