Monitoring

[Geoscience]

I have an ibook 600 dual usb and use Live 1.5. in osX. I also use an imic for my sound output. My question is what "reasonably priced" external usb device do I need to get that allows for sound output and for monitoring? You would think I could monitor my samples through the headphone jack on the ibook and use my imic as the master out. Unless I'm doing something wrong, it just dosen't happen. Thanks in advance for any input!