Zapco DC Intro - Manual (Page 26)

OEM Integration
Channel Summing: Sometimes you need to
combine high, mid, and woofer outputs from a
factory radio into a single full range input
In the Zapco DPN, you can sum 4channels or 6
channels into a single full range signal at input
1/2
Then all outputs that use input 1/2 will have
the same full range input signal
Sums Ch1/2 with Ch3/4 Sums Ch1/2 with Ch3/4 and 5/6
Speaker Level Inputs
: Each Zapco DC-Series
amplifier, and DSP-Z8 Processor has an input level switch.
In the Hi Input position you can attach RCA plugs to the factory
speaker wires and plug them directly into the Zapco RCA inputs.