I'd like to follow up on my post since there's been a recent development you might find interesting.
I ended up getting a TrippLite system big enough to power my whole studio instead of just the computers.
The model number was a SU3000XL. I should have paid really close attention to this: If you remove the capacity rating, the model number becomes "SUXL" which is short for 'SUX Lots'.
Just about everything I hooked up to this thing BUZZED. Not in the audio, but acoustically. Several of my microphone preamps were the worst offenders, but so was my control room power amp. So it would seem, everything with a toriod power transformer would "sing" when running off the tripp-lite, but be perfectly silent when on commercial power. Nice eh?
They sent me a second unit -- same problem. They won't let their support techs talk to the engineers, such a shame, so I was unable to further diagnose the problem directly with Tripp Lite. I worked with both Eric and Dave at tripp lite who were very helpful and kind, but in the end could not solve the problem.
One of my preamp manufacturers I had the trouble with agreed to receieve a Tripp Lite unit and do all the work to diagnose what was going on -- mind you this is waaay beyond the call of duty. Tripp Lite set up the demo, and then called the preamp manufacturer back (a manager, I assume, named 'Michelle') to say "we are not in the business of shipping units out to solve someone else's problem!" What?! You mean the fact that three different preamps ranging in price from $2,200 to $4,000 and a $1,200 control room power amplifier humms constantly because the output of your so-called pure sine wave UPS is so far from clean you don't consider this your problem?
I don't care what a UPS manufacturer says, when gear runs better off commercial power than the double-conversion UPS that claims pure sine wave output, that's a problem!
Funny enough, the preamp manufacturer (a smaller boutique firm of well respected gear) simply said "You shouldn't worry about it. Our power supply completely reconstructs the power within the unit anyway. We ship to Japan and don't make single change even though they run at 100v and it's 120 in the US. We designed filtering out commercial power into the unit -- it's unlikely you would have seen any performance improvement running on "perfect" power vs. commercial anyway."
Man, that's why I spent good money on good gear!
They then added Tripp Lite to a "Do Not Use With" list.
At least Tripp Lite call-tagged the "replacement" unit. I was pretty pissed when I found out they expected me to pay the $90 it costs to ship one of these heavy beasts myself. In the spirit of honest disclosure, they finally did agree to pay for the return shipping. The other one was returned to the place I bought it. So, all I ended up out was some time and the $400 I paid an electrician to install a now not-used dedicated 30A circuit.