Mystery switch


I have an old Audio Reflex receiver (Model AR-800) which has a 'DE. EMP' switch on the back: 75uS to the left and 25 uS to the right.  The 'u' actually has a preceding tail on it, so its probably a symbol. 
What does this do?
Also, it says on the back 'Do not use speakers less than 8 ohms'.  Is this as imperative as it sounds?

Thanks, 
128x128sound22card
The power supply rails ,transformers are small that is why it cannot handle lower ohm loads .never heard of this receiver. How old is it 
I would not invest in it ,no where to modify it properly ,which you 
would need ample space on any decent aftermarket parts which are all much bigger.