If a passive control is built into a power amplifier or integrated amplifier, that's the best place it can be! By doing so, the designer is able to bypass most of the problems that make external passive controls problematic.
An early example of this is the Dynaco SCA-35 amplifier, which to this day is a great starter amplifier (of course, with refurbishment and updates). Essentially the only active circuits in it are the phono preamp and power amp sections- the volume, balance and tone controls were all passive and the power amp itself made up for their insertion losses.