Playthrough doesn't work

I have selected Playthrough and I get no sound even though I see the sound waveforms in the Audio Tracks. I am able to play music on iTunes so my audio system works. I am using a Sony USB turntable.

While you’re in preferences, Go to Devices and make sure Audacity is set to play to your headphones.

My System Preferences window does not have Devices. My iMac operating system is Version 10.6.8.

Koz meant Audacity > Preferences. Then make sure that in Recording Preferences below that, you have Software Playthrough enabled.

If Software Playthrough does not produce audio, get LineIn .