If you haven't bought anything yet, check these out. Digi-Key part number 102-1007-ND. The CUI encoders in the upper left-hand part of the catalog part linked below. Kevin Watson (
kevin.org/frc has posted an excellent ISR example that makes it very easy to decode the ouput. We got it working and coded in less than 5 minutes.
http://dkc3.digikey.com/PDF/T041/0996.pdf