Does this help?

Yes, except for one question.

You said:

A linear regulator will essentially dump the excess voltage as heat.

But then proceeded to explain that the empeg used a switch mode power supply. Does a switch mode power supply also dump the excess voltage as heat?

I've noticed that the player will run hot or cool depending on which AC power supply I've got it plugged into, and sometimes it will also run hot in the car. Is that because sometimes the car or the AC adapter is supplying more than 12-13 volts?