Resampling live 3 with 404

My current setup is my piano, bass, guitar, 404 and live 3 going into my onyx 16 mixer on their own channels. With the onyx 16 monitor channels, i can send the audio of whatever i choose out. I have been sampling everything through my 404. Now i have the live 3 and im sampling that into the 404 but I want to send the 404 audio back into the live 3. I tried using a TRS cable from the 2nd monitor channel of the onyx into the live 3. I immediately got tons of feedback when i used any FX. The goal is to not have to pause and mess with anything to get the sound going. If i have a loop of something i played on the 404 going with FX i would like to be able to control that sound from the live 3 at the same time.