My 2 channel preamp has a bypass where the AVR/AVP plugs in, and those go out to the 2 channel amp when the preamp is off.
When the preamp is on. Then I can select a CD or TT input.
Of course one could just run the AVR/AVP into one of the preamp inputs, and have the 2 channel preamp set to a consistent volume, and have the preamp on.