Each channel. Which means the factory does go through a driver matching process.
1) Get a Digital Multimeter
2) Turn the dial to 100-200 ohms setting, or auto range.
3)Touch the leads together and write that down.
4) Connect the leads to +/- on one side.
5) Measure, and subtract the offset of the lead's impedance from #3.
6) Repeat on other side
7) [optional] Post your results here.