USB Ext Sound Card Vs. Squeebox

Forgive my ignorance - i just got a Paradisea for Christmas and wanted to try it with a Squeezebox, Airport Express and straight from a Macbook Pro and was hoping to tap into your expertise - (1) how do you output from iTunes via the USB and (2) what are the best music players (Mac compatible) given the shortcomings of iTunes 7 for high bit rate files? i assume more sophisticated players probably make it easier to output via USB to DAC. thanks in advance.

Thank you - this is very helpful. I will try this.
I've heard FLAC files are the way to go but not supported by iTunes is major drawback.

I followed your instructions and the USB connection to the Powerbook works - fantastically easy setup following your instructions. I then tried using a Toslink output from an Apple Airport Express I have been using to-date prior to the Paradisea. The Toslink connection did not work. Furthermore, on the back of the Paridisea is a small toggle switch that appears to be an input selector for the Paradisea, with one side pointing towards the toslink and one towards the USB/RCA inputs. The Toslink didn't work regardless of where the toggle was and the USB worked with the toggle on both options. This makes me wonder if the Toslink input works at all. Any suggestions?
Another question - does it matter how long a USB chord one uses is?
Final question - the Paradisea is picking up radio signals. I tried pulling the ground in the power chord by using an adapter but still picking up faint radio signals when the music is quiet/off in the Paradisea.
Many thanks for all the help.
Lloyd