If you’re broke like me, you were probably sad when you realized that the Griffin DJ cable only allowed for mono output and mono pre-cueing—it essentially just connects the left audio channel to both sides of your headphones and the right audio channel to both sides of your PA (or maybe vice versa?)
Well, I’m happy to say that djay for Mac works FLAWLESSLY with this little $9 gem from Amazon.com: Syba SD-CM-UAUD USB Stereo Audio Adapter. Once you plug it into your USB port, djay instantly recognizes that a second sound card has been added and asks if you want to use it for pre-cueing. Then just plug your headphones into that device and your PA system into your Mac’s headphone jack, and you’re good to go!
PRO TIP: you can’t adjust the volume on the USB adapter, and it’s REALLY LOUD, so you might want to switch your audio routing so that the main mix goes there (since you probably have volume control on your PA rig) and plug your headphones directly into your Mac’s headphone jack, which you can control with the keyboard volume keys. It’s rated at 44.1 kHz, and I can’t distinguish any difference in the sound quality from one to another.