I too hope this is followed up as it is a very interesting problem.

I have suffered similair symptoms on a project. Coaxial digital audio from a Sonos ZP80 running about 60 metres along cat5e to an AVR in a rack. When the light switch for the room was operated the sound would drop out and return in a matter of a second or 3. Of course it didn't happen every time but I did know that the cable run for the AV was fairly close to where the cables for the light switch were - the sparkies had run the cables on this project and had a tough time keeping mains and AV apart.

My question to Sc0tty is this; you have not mentioned cabling between components on this job. Perhaps there are none in the fabric of the building - just interconnects between stuff on shelves or whatever - but if there are runs around the house they could be picking up strong RFI from the switches and an alterative connection method may help.