For integrateds not equipped with internal monitoring circuit, separate preamp and power amp give a much easier possibility to use a sound processor, managing ALL multiple “sources” used by the listener and connected to the inputs of the amplification block, by means of inserting a processor between the preamp and the power amp.
In case of an integrated not equipped with internal monitoring circuit, such an operation needs a separate input selector to put between the “sources” of the listener and a LINE level input of his integrated.
More: in such a case, the direct signal from a magnetic cartridge of a TT can not be sent to such an input selector, only via the internal “phono stage” of a TT or a separate “phono stage” between the TT and the input selector.