Does a brand new electrical circuit for audio gear benefit from burn in/break in time?

I'll wager not one of the respondents fully disconnected their system and re-connected prior to the miraculous improvements...

- not sure why you would even conjecture that … but in any case …nope … that is dead wrong … and you lose that wager …full stop. 

- My entire system was fully disconnected into its individual components and then boxed up and stored away for protection during the house renos

- after full Reno completion six-odd weeks later …THEN …all boxed up components and cables were taken out of storage  and finally reconnected again with new dedicated line and outlets  …. and voila … 

Actually, I win. 

Six nines of the time people make changes, they do not reseat all connections, power and signal, before experiencing night and day improvements.

^ +1

Unless one lives in an ice box, flipping on the HiFi and playing a track or two while brewing an espresso, pouring a malt or similar, gets the circuits close to idle temperature or better. [class A excepted]

Unless the power amplifier is defective, voice coils & passive XO are at ambient temperature. Temperature changes in these may have more sonic impact than the electronics.

For the vinylphiles, exercising the armature may also benefit.