I would also plug direst into the effects loop of the amp with your guitar, or some device to see if audio is traveling through this return input. You could test it with your thumb on the end of the cable, boost the level with a drive pedal to at least match the front of your gutar amps input volume at about 1/2 volume. I quit going into my return and use the front input to utilize changing the eq on the fly. I found reducing the mids and treble to 2 on the dial and bass at 5 and it flattend out the eq to match the tone of the guitar straight into the return. My method, works for me. All of my patches use the cab sim. live, I do not have any pretty sounds
This is what it sounds like from a studio environment (could not embed the soundcloud link)....but this eleven rack is hard to give up there is so much in there. I have not been switching patches for over a year now, I just go up and down on the guitar volume to change tones.
Hope you find a solution!