Originally Posted by afsar
My PDX-5 will only accept line level input i.e. low level rca input, if you feed it speaker level input it will be too loud. Not sure if this answers your question.
My HU is coded to hi-fi so signals are low level flat signals from the HU.
Other than high and low levels, it is differential balanced (not 3 wires system though) input which is restricting us from having any amp in our cars.