Technical Question About Powered Speakers

I am using the Audioegine HD6 power speaker system.  It has two mono linear A/B Class amps in the Powered speaker and it connects to a Passive speaker through a single positive/negative speaker cable.

From my understanding, the linear push/pull type of system it employs is that the audio signal travels out of the Powered speaker through the positive terminal into the positive terminal of the Passive slave and exits out of the negative terminal of the Passive slave and into the negative terminal of the Powered speaker. 

I understand that you must complete the circuit for there to be sound. However, what happens to the return signal on the negative terminal on the Powered speaker?

So, the input audio enters the built in pre-amp and is moved to the two amplifiers. Obviously, the cross over is built into that same audio pre-amp/amp board. Since one amp amplifies the left channel and the other the right, then how does the system send the audio signal linearly? That's really question number one.

Also, when the audio signal is sent out over the positive speaker cable to the Passive speaker, its cross over sends the signal to the drivers. So how do the drivers send the signal back to the cross over and out of the negative terminal? Is it just left-over charge?  Is it diminished audio signal?  How does that signal affect the performance or functions of the Powered speaker? This is the second part of the function of this configuration I don't understand. 

Thanks in advance for any help. :)