ARC Ref 6 - Is it normal?

Yes, I find this on Ref 6 user manual page 5. 

Quote:
When sensing low line voltage, the preamp displays “Low Line” and automatically goes into “Mute”. This condition will persist until the line voltage returns to a safe operating level,. The unit will remain in “Mute” even after “Low Line” no longer appear. 

A conditioner doesn’t do anything if there’s an issue on the other side of the outlet.

That depends on the power conditioner. Some can regulate AC voltage and thus keep it at a proper level even when the line level is low.

The low voltage may be the AC coming into the home.
The powerline may be bad, the power company transformer may be bad.
Are you in a city? or out in the country? Suburban?
After checking the voltage coming in and verifying it is low when it enters your home.. you might call your power company and ask about it being low?
You may need a new local power company transformer, or the wiring outside is being touched by trees etc..
These things should not be charged to you if they need fixing.

I aware this low current problem came from a heater was using when I switch on my Ref 6. And I just check this heater, the output is 1,000W !!
When I don’t use it, there warning message does not exist from my Ref 6. Everything is clear now. THX!

Check and make sure your ac cord is fully plugged into the back of the ref 6.
I also had this problem once fixed it by fully inserting the 20 amp pc cord.