Thanks for your response. I have looked all over the file 'test.c' (which I obtained from the 'line_follower' project in the pololu avr library in the atmega328p examples) for the definition of read_line(). I have searched this code, and all other related analog libraries, including the PololuQTRSensors library, and have never seen an actual implementation of read_sensors(). I may have easily missed it, but I looked for quite a while before I gave up. Anyways, I have managed to solve the issue and can now read individual sensors by playing with the code for hours on end. There's not much rhyme or reason to this solution but it works.
You must run the 'auto-calibration' routine where the motors spin back and forth for a few seconds, and then one must call the read_line() subroutine afterward. The read_line() subroutine has something to do with 'arming' the sensor. After that, meaningful data populates the program by using the calibrated_value[i] array.
Hope this helps someone somehow.