Question Ceiling speakers

Jan 11, 2024
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I'm a complete novice by the way, so apologies in advance if my terminology is incorrect.

Moved into a new house where our family room has 4 B&W ceiling speakers, 3 speaker wires coming from wall (where TV would be hung) and two sockets on the wall with 4 pairs of connectors each - second set's 4th connector is RCA the others being for banana. Identified all 7 banana connectors relate to the 4 ceiling speakers plus 3 for the wall speakers - not sure what the 8th RCA connector is for - only one wire connected to red input behind it. I've tested the 4 ceiling speakers with an old Denon amp using speaker cable from the amp to banana connectors into the wall sockets and managed to get one speaker (front left) sounding pretty good but the others, although they did connect, were very thin tinny sound with no bass and very low sound volume. I've looked at the wiring behind the sockets and all have speaker cable connected except the eighth connector which has a thick grey cable coming from from the red RCS connector only.

Anyone any ideas on how I get the other three ceiling speakers to have more of a full sound?
Any ideas on what the grey cable (4th RCA connector) might be for?

Any pointers would be greatly appreciated.