Use FX buttons then send each desired channel amount to that FX.
For FX>mix busses. Select the mix buss then select the top layer button. Bring up FX return as desired for return amount. Do that for each buss.
So the idea is your input channels are sending to the FX then you go to each buss and bring up the return amount for that buss on layer 3 or 1 whichever you consider it. The top row.
Hope that helps.
George
Mid America Communications AV.