Good. Pleanty of I/O's memory and multipliers. You'll have to create a couple of interfaces, for the A/D conversion. You can try an A/D chip ( or 1 for each string ) or else you can cheese out and cobble up a 'homebrew' A/D using discreete components. On the output side, you might connect a D/A converter, filter, amp... or interface the resultant output to a PC so you can use the sound card. Sounds like an interesting project.
PS: I forgot you are using an optical pickup. There is probably no amplitude information, only pitch ( frequency ) information, so forget what I said about A/D conversion. If you set your optical system up smartly, there will be no reason to convert the input signal, other than to extract the frequency information.
ahhh thank you for that hint. My partners wanted to get the pickup playing through a speaker( so we will definitely have something working ) so its not currently set up like that. : ^ )