I found this googling. The discussion was for a PDX 4 but I assume it's the same. Can anyone confirm? The Y-splitters don't make sense to me. Why would Alpine engineer it that way?
Inputs: use 2 "Y" RCA adapters, one each for the left and right channels, i.e. your left RCA coming from your HU will be connected to both CH1 and CH2 inputs, the right RCA coming from your HU will be connected to both CH3 and CH4 inputs.
Outputs: left channel will be the + terminal of CH1 and the - terminal of CH2, right channel will be + terminal of CH3 and the - terminal of CH4.
