Help - Mac Mini not sending audio via usb port

I just bought a new mini and transfered music from a laptop with windows xp to the mac. When I run itunes on the Mac, the internal speaker of the Mac put out sound but my main audio speakers did not sound (dead silent). I have the Mac USB to PS Audio DL3, then from the PS Adio DL3 to the integrated amp.

When I replace the Mac with the Dell laptop with Win XP, the system works so it is not a cabling problem the DAC or the amp. Do I have do some settings on the Mac OS Leopard? Itunes on the Mac? Somehow the music stream does not come out from the Mac mini usb port.

I am also a Mac newbie .

Just in sure you change your mac prefs to output to's either one or the other speakers or USB...

Go to prefs, click audio, click usb audio Codec...and you should be fine...else I'd double check you DAC is set to USB and not opt or coax...and your proper source is selected on your Integrated. be more exact...go to System Preferences (the gear box looking thing on your launch...if Using Leopard...and click on Sound...then do above.
Altrnatively, find the Audio MIDI Setup panel and put a copy in your Dock.

You can select the Output directly from it. Note that the USB driver will not appear until the USB device is plugged in and on.
I went to pref/sound but all I see is the internal speaker. How do I get to the USB audio Codec selection? Again, I am Mac-challenged.
I think CKorody is on to something right track...If not an option, sounds like it's not "seeing" your dac yet...make sure the USB cable is in all the way (both sides)... contact me if you'd like...I'll try to help.
Fixed. Thanks to all.