source + preamplifier + amplifier + speakers = > sound
or
source + integrated amplifier + speakers = > sound
an integrated can play the role of a preamp to an amp (since it has to have the preamp functions) and can play the role of an amp to a preamp (since it has the amp functions)
Generally, you are better off with an integrated if you are not into tweaking and spending 1000s. Your best bang for the buck will be speakers with what you have now.