Hi Mark and welcome to Beoworld!
The BC9000 speaker 1 sockets will accept 4-pin DIN cables like the ones available from Steve. The extra two pins on the BC9000 speaker 1 sockets are to provide data to the Penta speakers. This enables the display on the Pentas to show Volume and Source. Speakers without displays should work fine without the two extra connections.
Location: Warwickshire, UK
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