High Level Inputs - Speaker level inputs are commonly referred to as high-level inputs. It will be used to connect the US10K to your factory radio or an aftermarket radio that does not have low-level (RCA) inputs
Low-Level Inputs - Line level inputs, also known as RCA inputs or low-level inputs, use RCA interconnect cables to link the US10K with the source unit. Most aftermarket radios have multiple pairs of RCA outputs that can connect to multiple amplifiers