Not the answer to your question but a solution to your problem: PS audio regenerators provide adequate power to prevent the problems you are having. I have a PP10 for a 200 watt system (200 watt draw, not 200 watts to the speakers) and it sounds great. the PP10 is the old generation, lots of heavy copper windings, lots of instant power to your amp. It has zero output impedance to slow current to your amp. Your Niagara says "low impedance" but doesn't publish a number. Based on your experience, it isn't low enough.
You may have read my repeated warnings about power conditioners, surge protectors, and even some expensive devices (such as your Niagara) that significantly limit your amp. So I'm not a typical guy who spent $5k on a device so it must sound good.