1 pointWhy not connect a cypress fx2 board to the gpio? Boards with them are cheap now. They can sample 16 bits and send over usb2. At 30MHz you will saturate the usb2 bus (actually before since the host requests first). You will need to write some 8051 firmware for the fx2 and a driver for the PC. What are you hoping to do? One way transfers from fpga to PC or something more complex.
1 pointI don't think the Papilio Duo has USB. There is a USB serial chip as described here (http://papilio.cc/index.php?n=Papilio.PapilioDUOHardwareGuide#PProUSB). So up to 3MHz via serial. I think you'd need to connect a USB2 chip to the GPIO to achieve this. I've had success with usbhostslave, usb chip + some resistors, but that is only 1.1 speeds.