You are advised to choose the darlingtons load resistance so that the 500mA absolute maximum limit is not exceeded.
A late reply but hopefully not too late: You should never ever go near the absolute maximum ratings for any component !
Doing it is begging for trouble
Read the fine print slightly below in the data sheet:
Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
So in this case do not exceed 350 mA per channel.