Best way to have wireless music is to purchase an Airport Express. You can find them on eBay if you don't wanna pay full price, but imo well worth the full MSRP.
Also, the USB port on the ATV2 is a 'mini usb' port for maintenance.
As far as the audio cable, I suggest you just buy an optical cable, either from Monoprice or Amazon, these cables usually start at $5. I have a generic toslink cable and a Monster optical cable and I can't tell the difference whatsoever.