"I don't see any advantage connecting the IR-sensors to an A/D converter."
Look at Jay's schematic. He thought it is important to set the 1/0 level via a pot. He also said that the sensors needed different levels. I thought with fewer parts on the board maybe he could get the auto router to work.
I do not know what IR-sensor he is using. A line flowing project, using digital, only knows line/no-line. An analog line flowing sensor can indicate percentage of line. "About to fall off the line, make small correction."