Isolation Transformers: my experience and concerns

Recently, I found some old threads discussing the merits of isolation transformers.  Brands mentioned were Topaz, Xentek, anything with stated low interwinding capacitance.  I am not an EE but was intrigued so I bought a used 250VA isotranny made by Magnetek Triad.  It seems to be well-made but doesn't have stated interwinding capacitance.  My amplifier is and always will be plugged directly into a wall outlet.  All other equipment, DAC, pre, phono pre, transport are plugged into a 6-outlet distributor (NOT a conditioner!).  Placing the isotranny ahead of only the preamp had a very significant and positive effect on the sound.  Everything became much clearer and cleaner sounding with better focus, separation and depth.  Naturally, my audiophile OC behavior led me to purchase two more isotrannies:  a 500VA and a 125VA same brand.  Btw, these are not toroidal transformers, they have separated primary and secondary windings, and all are 120VAC in/out.  Currently, I have the power distributor plugged into the 500VA.  The DAC is plugged into the 125VA which is plugged into the distributor.  The preamp is plugged into the 250VA which is also plugged into the distributor.  My system sounds great!  My opinion is that this is probably (definitely?) overkill but is it safe?  These front end components all draw about 10W of power.  Again, my amp is plugged directly into the wall.  Thanks for your opinions and comments- I can handle it :-)
Lots of technical expertise from posters here:

That's quite a thread.  Thank you, Randy.
yeh, makes my head hurt

Luckily, I know the speakers and the room matter a lot more...

anyway, my tentative summary is:

medical transformers cost too much

use a Topaz, and buy it used
Yeah! It's right. Placing the isotranny ahead of only the preamp had a very significant and positive effect on the sound.

Isolation Transformer in India | Toroidal Transformer in India
Currently, my preamp is the only component plugged into an isolation transformer.  I concluded that this was the best combination and removed all other isolation transformers from my system.  Interesting that you found the same results.
I bought a big Torus and plugged everything in it, incl tubed mono blocs.  Previously I had several very good passive filters (big Lessloss, Acoustic Revive, Stealth, and Bybee Holographic).
Since I have the Torus I never looked back. 
IMHO you should be 100% isolated, or 100% not isolated from house power. I am a big proponent of isolation transformers, the higher quality the better because some are noisy.

Tripp Lite makes a good isolation transformer. This is a great way to get clean(er) power if you don’t want to swing for a PS Audio P5/P10.

TrippLite Medical Grade Isolation Transformer 1000W -
PS Audio Power Plant P5 -