Sorry finally got my answer.
These units would accept a two-channel signal from the output of a preamplifier and synthesize up to three additional audio channels. The left-front and right-front channels - the original two-channel source - were also modified by the processor. The line-level outputs from the processor were then connected to power amplifiers, one channel of amplification per processor channel, which were used to drive the speakers
Stereo system with sound processor:
Source >> Preamp >> Processor >> Power amps (5) >> Speakers (5)
Some processors also included three power amplifiers for the centre, left-rear, and right-rear channels. The two-channel audio signal from the preamp was connected to the processor / amplifier. The processor / amplifier's right-front and left-front channels line-level outputs were connected to power amplifiers to drive the left-front and right-front speakers and the speakers for the centre, left-rear, and right-rear channels were connected directly to the processor / amplifier.