MPC expansions are built to be used in MPC Beats, MPC 2.0, and standalone MPC's.
Depending on your operating system, they will be found in the location listed below.
MacOS:
Library > Application Support > Akai > MPC > Expansions
Windows:
C:\ProgramData\Akai\MPC\Expansions
C:\ProgramData\Akai\MPC\Expansions
The audio files are organized into MPC format drum and instrument programs, and the raw audio files will be found in the folder labelled "content" in the locations above.