Has anyone tried using a double UPS for clean power?

If you mean daisy chain UPSs the answer is NO.

I was confused on that point as well - it's NOT daisy chaining two UPS units, which would not be beneficial. It's a single UPS unit designed to internally convert the wall AC to DC, and then from DC back to AC (hence the "double conversion"), with a parallel battery supply in the middle to provide seamless continuity in case of a power outage. Sounds much like a power regenerator, plus the battery backup.

You can say it's not a good idea to run a powerful amp off it, which is true, but many audiophiles advise the same even with powerful regenerators (like the kind PS Audio sells). Plug your amps right into the wall, IMO. 

In the past 40 years I've never had a single device - even the cheapest disposable crap - damaged by a wall surge. I've also had an AQ Niagara 7000 and decided last year I could live without it (I can).

Video is strange- asking a manufacturer for free advice to cheaper alternatives.  

@kennyc 

I found it odd as well, but it made me wonder if anyone else had tried it and if it really worked. For a few hundred bucks could l really get clean power and would I notice a difference?

@mulveling 

Two houses ago, I had a lot of noise on my power and I lost a TV and a receiver during a storm.  I bought an Audience AR6.  It made a very noticeable difference in my system.  We moved from the city to the country into a new subdivision on what used to be an open field.  Everything was sounded great even without the power conditioner, but after a while, I put it back in because it had a magnetic circuit breaker. About seven years ago we moved back to the city, and near a four story medical building.  Most of the time my power seems fine, but every now and then my system sounded different, kind of thin. I put the AR6 back in and it made no difference. And once again, I left it in because of the magnetic circuit breaker.

@mulveling  I haven’t had coffee yet but isn’t that how all regeneration works. AC > DC > AC? So what's a "double UPS" the OP mentioned?

It’s a single UPS unit designed to internally convert the wall AC to DC, and then from DC back to AC (hence the "double conversion"),