I'm not sure if it's theoretically possible, but the explanation I've heard from at least one high-end audio company is that their components need some time to break in because it takes time for all of the capacitors to fully charge. This at least seems scientifically explainable. Not sure if capacitors can, themselves, break in (have a higher total capacity after some amount of charging and discharging), but such action might explain an audible effect.

Not an engineer by a long shot--I'm just throwing a theory out there.