so I have a 2002 A3 sport with the Symphony stereo option. it sounds great but the cassette deck doesn't get much use and the 6 stacker is a bit inconvenient. I want to know what the options for fitting a USB port are as I don't really want to change to an after market head unit. Any suggestions? 

Hi Chris....welcome to the Forum

I would definitely go for an aftermarket unit as the available functions in them are way better than the standard fit unit...although not sure the sound quality would be as good.

Give these guys a try   http://www.iceboxauto.com/audi

Cheers  Trevor

Hi Chris 

a after market head unit would be some much easier to install as just trying to fit a USB would be a night mare! I'm just about to have a double dip unit fitted in my 2001 a3 and they do look really good! And they do have USB, headphone jack and Bluetooth! 

Thanks for the replies guys. Any decent looking head units start to get pretty pricey though. What about the in line usb/Bluetooth devices that plug in the back? They go for around #80ish on eBay. Any ideas about those?

I think Halfords sell Pioneer systems for around £80 with all the bells and whistles

New stereo in. I went for a JVC double din unit costing 90quid then another 70 for wiring harness and facia plate (which took some modification). It's finally done and it works. Thanks for helping me decide what to do.