I have a Pansonic stereo system with separate high and low speaker
terminals. There is only one stereo power amp ... thus it is not a true
bi-phase arrangement. I can't find the answer to how the hybrids work, so I
am posting my guess here.

Here is what I think is going on. The right channel is phase inverted when
compared to the left. Thus, for a mono signal, the signal voltage across
the R-L connection is twice that from R to gnd or L to gnd. The clue is
that the low speakers are series connected across the R-L hot terminals and
so are the surround speakers.

Anybody know for sure? Thanks.