To connect an external effects unit to the UB1202, follow these steps:
1.) Use a cable to connect from the FX SEND port to the input of the effect processor.
2.) Then connect a cable from the output of the effects device to one of the LINE ports. If the device has stereo outputs, you can use both stereo line inputs (5/6, 7/8, etc.)
3.) Adjust the the effects processor to 100% wet.
4.) Turn the FX knob on the channel you are plugged into all the way down (to avoid a feedback loop).