Using step up / down transformers?

Not too much oversized though. 30% more VA than you need is a good amount.

This statement isn't quite correct. AC power transformers will generate distortion, particularly if loaded past about 50%. So to prevent the transformer from distorting the AC line waveform it really should not be pushed past 50% of its total rating.

GOOD transformers will not degrade sound. +1 millercarbon, there is a reason they are still used today in audio. I always double the power requirement specification of the equipment to get the power rating of the transformer.

@cleeds, 
Sorry I was not clear:
I know the power goes through multiple transformers as part of the electric grid's distribution system before it reaches the transformer in my neighborhood. I know my audio equipment has transformers. I meant by adding transformers to the main AC power lines/branch circuits, from the electrical panel in my house to the audio equipment in my room. would be sound degrading. i.e. step up / down transformers, bucking transformers, power conditioners, AC regenerators (none of the former are on my audio lines)
Yes, my audio equipment sounds better on 240 volts. I plug all my audio equipment directly into the plug. That has been my experience. Audio manufacturer, Emotiva thinks audio equipment sounds better on 240 volts. See the link below. Page 10 section 7 regarding IEC power cord.
BTW, 240 volts, double phase is more efficient then 120 volts, single phase. Maybe ask Jim jea48, about voltage and amperage. Maybe he can explain to you better then I or show me where I could be wrong. Mike

https://cdn.shopify.com/s/files/1/2572/6926/files/XPA_HC-1_User_Manual_v10.pdf?30550

I am using ACUPWR step up transformers to run 230v subs /CD/DAC. Heavy duty build quality. Sounds identical to native 230v when the components were used in Europe.

ditusa

... 240 volts, double phase is more efficient then 120 volts, single phase. Maybe ask Jim jea48, about voltage and amperage ...

No, 240VAC is not more "efficient." Your equipment will operate at the same efficiency at either 120 VAC or 240VAC - and it will consume the same amount of current either way. Feel free to measure it for yourself.