Processor or DSP?

I am developing an Inkjet printer, wherein I need 16 GPIO pins to be able to run signals at 8 nano seconds. Can you please suggest the best processor or DSP with appropriate Evaluation kit to get this.

I started off the project using the P2 Parallax microcontroller and got caught when I had to develop signals for the inkjetting controller. We are working with Funai color inkjet cartridges.