zapco Reference Series 2 User Manual page 54

Reference 360.4 Special Features
Another difference is the SOURCE SELECT switch. The 4 CH
position is used if you will have separate front and rear channel inputs. This
is necessary if you wish to fade between front and rear. The 2 CH mode
allows the front inputs to pick up their signal from the rear inputs. This lets
you run the entire amp on only one set of input cables. This is very useful
when running the 360.4 in 3 channel mode or when using it as a stereo
amp. The 2 CH w/BASS mode is similar to 2 CH except that the rear input's
bass boost circuit will affect the front input as well.
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