on one page you have the power amplifier section, drives lines are just a name to the driver section of the second page
there was not enough place to put all the schematic, drive line could be called pre-driver section etc ...
the "output" line is returned to the op amp TL074, who provide output feedback to the pre-driver section, and another op amp section for the error detection ...
q501 is your Bias transistor, it should be placed on the heatsink ? or at least be in contact with