The interfacing of quadrature encoders is application specific - issues like the speed and number of counts are critical. What works for a standard computer mouse may not be acceptable for a servo controlled motor. You may wish to try www.agilent.com as they have encoders and the interface ics. They also have a few application notes that may be of assistance. I also recall that microchip had some app notes for their PIC micros - there may be some info of interest.