Word of caution about
absolute encoders with the Talon SRX... most of them that provide analog output seem to require 5v power instead of 3.3v power which the Talon SRX must have for analog input. DO NOT connect 5v to the Talon's analog in. It might not end well.
CTRE is releasing a converter board and we are making some custom ones. We have a student working on a write-up of how we created ours along with details.
It might be neat to see the Talon SRX controllers support
gray code in the future in addition to analog output for absolute encoders but that would likely require a firmware update and some serious coding witchcraft for the Talons.