Obviously not commercial grade equipment or even equipment intended for use with microphones. Looks like they just threw a microphone mixer on a home stereo receiver.
I think you are going to find a problem is with leakage in the receiver or tape deck. This may or may not be abnormal by the way, considering what this equipment is.
Remember this is home stereo stuff and is not meant for commercial use as a PA system with hand held microphones. Consumer audio equipment is not subject to the requirements that commercial sound equipment must adhere to. Things like three wire line cords and minimal leakage for instance.
Actually being an electrician and being familiar with the code may come in handy. I think you could make a case for this equipment not being listed for the use. Probably the only way you are going to deal with this and make it safe is to get them to replace it with the proper equipment.
-Hal
