when one supply goes the opposite rail turns off as well, its the design. that is a good design as well, so knowing which one is off is not really beneficial, its both!
this sounds like a dual supply system. Failure may occur in these systems with the regulation of the two power supplies wandering away from each other over time and the current sharing not being shared, the load consequently shifting to only one of the supplies and failure following. Please check the balance of these dual supply systems over time (say every two years).
Power conditioning is usually not a bad thing, but to get an adequate conditioner for a larger SSL board is no small task. I have not really tried to figure out the minimum requirements, but it would be on the largish size. To me, 3kw is not largish.
I have always liked Superior Electric Co. Stabiline voltage regulators, not cheap and some people don' like the system architecture. But they can be hooked up to do the whole studio, able to be ordered up to 2150 Amps! as well as more reasonable levels. I have built several sites using these units, mostly they were industrial sites (radio transmitters) but also one studio. Everyone likes the constant 120Vac at all times and the clean power it provides.
The only problem I see is the more recent purchase of the company by Danaher, a company that I have little respect for. They have purchased Fluke and Tektronics among other tech companies. Not an innovative company to work for anymore, nor caring about the employee's, don't expect leading equipment from these companies anymore.
Alan Garren
link to Stabiline products (pdf)
http://www.danaherspecialtyproducts.com/uploadedFiles/Siteroot/Superior_Electric/Products_and_Solutions/STABILINE%C2%AE_Automatic_Voltage_Regulators/whrcat10-01.pdf
