Sigma-Delta ADC's and Thermopiles

I spent most of my day yesterday researching how to interface the ArduPilot XY sensor and the Paparazzi Z sensor to the Propeller. Upon registering with the Parallax forums, I started a new thread to help me along with my research. If you read the thread, you can see how things progressed and why I am trying to figure out how a Sigma-Delta Analog Digital Conversion works, or what it is for that matter, and how I am supposed to use it. Because the xy sensor has 2 analog output wires and the z sensor has only 1, for a total of 3 outputs, I decided to go with Leon's suggestion and use a multichannel ADC IC to handle the conversions, thus bypassing the need to make three of these things:

as described in a Parallax help document.
Now the search begins for an appropriate ADC IC.

First Post! And Introduction

This site is where I will record and journalize my attempts at a GPS Autopilot for an R/C Vehicle, most likely a plane. The Autopilot will be based around the Parallax Propeller. This project is something I have been wanting to do since 6th grade, and now that I am a rising Sophomore, I need something to go on my application for college. My current college of choice is the Massachusetts Institute of Technology in Cambridge, Massachusetts. I have longed to go there since the age of 5 when I was living in Concord.