I imagine the PSR2k is similar to the 740 as one replaced the other. I did some measurements on the 740 and the mic input has an additional amp with a gain of 5 which is switched in when moving the switch to mic from line. The sensitivities are 0.72mV mic and 3.5mV line for the green light(signal) to come on and 6.8mV mic and 50 mV line for the red light (over) to come on. The impedances are 50k for the mic and 10k for the line in. So your mixer should work just fine connected to the mic/line in and the switch set to line. It might be a little too sensitive so check the spec for the mixer line out level and adjust accordingly.

Bryan