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Denno you're thinking pairs, he only has a single pair of outputs, so he needs 'Y' adapters/splitters.
I don't understand correctly either.... Doesn't he mean he has two outputs from headunit (a pair) going to amps input. The other two on the amp should be a pair of outputs to go to another amp (daisy chain). With a pair of inputs into amp he can run two pairs of speakers as it's a 4ch amp. Unless he is planning to run more then one amp then he'll need 'Y' splitters or just daisy chain amps.
My mistake, I was thinking of mono amps for some reason, I forgot 4ch amps have two sets....
Won't it be easier just to buy another headunit that has more then one set of RCA's?.