Streets Electronic Systems Model 950 follow up question

I have what may be a more general question about amplifiers. The Streets Electronic Systems Model 950 in addition to the positive and negative terminals has another terminal (colored white) that says "Feedback Return".

What is "Feedback Return" and how is it used?

(I would include a picture but my camera crapped out)

The other "post" is an "input" that "siphons" the back electrical wave generated by a speaker into the negative feedback loop of the amplifier. This information is now included in the feedback loops correction and the amplifier theorectically will produce a more accurate waveform output. In the real world it was hit or miss with this setup. Some speakers sounded better both 90% of the time the best sound was with the normal outputs.