So, lets say you have the combo speakers at 8 ohms and an 8 ohm external cabinet.
Do you calculate the loads independently for each output channel?
First, for simplicity, lets say you wanted everything to run all the time, would you hook both the speakers and external cab to output A using both 4 ohm jacks of channel A? It does say "use with two 8 ohm cabs".
Next, and what most people would probably do, lets say you wanted to run the cleans (ch1 and ch2) through the combo speakers and the overdrive (ch3 and ch4) through the external cabinet.
Would you hook the combo speakers into the 8 ohm jack of output A and the cabinet to the 8 ohm jack of channel B? Or, do they need to both be in the 4 ohm jacks?
Is the load calculated independently for each speaker output channel? Can you run two 8 ohm cabs on channel A and two 8 ohm cabs out of channel B?