Sometimes... It depends on which ITCH hardware controller you use!

There are currently 8 controllers which require no external mixer. These  "all-in-one" controllers are:

» Allen & Heath XONE:DX

» Novation TWITCH

» Numark NS6

» Numark NS7

» Pioneer DDJ-S1

» Vestax VCI-300

» Vestax VCI-380

» Pioneer DDJ-S1

 There are also two controllers in the ITCH family that do require an external mixer. 

» Denon DN-HC5000

» Numark V7