When connecting the Korg Kaoss Pad, the sound can be output via either of the Two FX Sends provided. FX1 may be switched pre or post-fader, while FX2 is pre-fader.
The send is then routed back to the mix via one of the two FX Return inputs.
Connect RCA (phono) leads from the FX1 SEND on the mixer to the input of the Kaoss Pad.
Connect RCA (phono) leads from the outputs of the Kaoss Pad to either one of the FX returns.
(If you are only using one send, you can go out on FX1 and back in on FX2, or vice versa, but why complicate things?).
This configuration will work for any external FX input.