I get that because as maisbass said the inputs would have different coloration and loading. My test was with the Berg IPs. In that case there is only one input for the plate amp. I could plug either the Monique's line or DI into it.
Trying to interface the Monique into the AER was trial and error. The AER sounds great the Monique could make it better. The best was into the actual instrument input set to line. It can be set to mic. Into the pwr amp in, effects in etc. just didn't work.
It took a careful setting of the input to get the most Monique while not over driving input. Now it's set and forget. Hilarious at first gig I did everything but crank the Master so it was timid. After one song lightbulb moment. Crazy how live switching left to right to left brain troubleshooting/playing tune is chaos.