Power problem causing drop-out in surround sound

I recently moved into an old house (78 years old) and had 4 dedicated 20 amp circuits for audio - home theater system installed by a licensed electrician. My Sherwood Newcastle AVP9080 surround sound processor now drops out for a period of 1-3 seconds anytime anything is turned on or off throughout the entire house. The house does have updated electrical service. I have tried to isolate the problem down to an individual circuit by turning each circuit off individually to see if the problem still occurs with no luck. I did not experience this problem at my previous house (even older). I have had my voltage coming into the house checked by the power company and it falls within acceptable range (123V) and I have tried to using a multimeter to measure what happens when something is turned on and off with no indication of any problems. Can anyone tell me what to do at this point as far as things to look for, what other kinds of test equipment to use, etc. This drop-out only happens on digital inputs. On analog inputs, there is no problem. Also, my DAC for my two channel system does not experience any drop-outs.

Thanks,
Jim