[teetoon]

In the OP's second picture, there is a brown and black wire to the right hand side along with a brown figure of 8 cable which I suspect is the mains feed. Could the brown and black be the remains of the turntable feed ?
The speakers all seem to be fed from the top of the chassis so they are all accounted for and the extension speaker socket looks to be the red and black wires going to the rear panel socket board.

David.