Can't hear myself in headset mic on Macbook

Running Behringer XENYX 802 mixer with Macbook. I can hear sounds/music in mic but cannot hear myself. What should Audio settings be set to? Any help appreciated.

What software are you using on the MacBook?

(OS version and any other important details about the MacBook would also be very helpful)

Macbook 13" 10.5.8 2.0GHz/2x1GB/160G/SD Model Number A1728

And the software?

Spreaker, Garage Band. I can already record with two mics through usb. My question was how to be able to hear each others mic while recording/broadcasting while running through a mixer and high frequency amp. Have it working on Windows 7 64bit. I just downloaded software (LineIn) and am going to try that. Still open to any help.

Thanks,
Jim

LineIn may help, but it's just giving you the monitor capability that's already in Garageband