The way I look at it the whole piece of equipment is a sythesis of many parts that do their own things but do something a bit wonderous when working together. As one uses the device various electronic pathways and heat conduction routes come into action over and over again and at first the system needs to becomes stable, which takes time. This could even extend to subtle changes in resistivity, and heat causes changes in the dielecttric values ... All in all, after a week of running, if there are any problems in the sytemic behavior as a whole they should start to show up.
This goes for good speaker cable as well, though its not a matter of problems showing up, just stabilization.
Speakers need break in, which is partly electronic, as above, but also mechanical, dealing with the stress in vibrating membranes, stretching rubber, heat expansion...

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"Art is not a mirror, but a hammer."