I have tried lowering the Send level. I could not eliminate the clipping on the rack mount delay that I had for many years. I had other rack mount systems that I could not use with the Mark V. All of my effects that I used to own prior to the Mark V were ideal with the Mark IV and I did not have any issues with that amp regarding FX loop. Most of the effects I did have were given away or thrown out since that gear was from 2000 or earlier. Bought a few pedals starting with the Line6 DL4 sounded okay even with the compression but was not really suitable for the Mark V. Tried the TC Flashback X3 and that one was about the same, compressed delay tone. Both work well with the other amps. Then came along a Strymon DIG, no issue there using it in the Mark V loop and also the other amps as well as the mixer board which has two FX loops. I believe that one does some sort of auto shifting on the input buffer or on the output as it can take up to +8dBu signal. Works just as good with the instrument level loops of the JP or TC-50, Roadster and RA100, including on the front end of the amp. So Strymon got me interested and now I have a few more of their products. Ola, Big Sky, Brigadier, OB.1. What also works in the Mark V loop is the Boss Terra Echo. Also have a Boss PH-3 phase shifter but have not tried that in the loop. I no longer use the line6 or TC product that I have at the moment. However I still need the Ebtech LLS so I can slave out to another amp that does not use line level loop (roadster). I think the LLS would improve the slave out function better using the FX loop with an isolated signal splitter (allows you to keep the power section of the Mark V and to send FX signal to another amp but if the signal level is too strong it will not sound ideal). I have a Lehle P-Split II that is awesome for bi-amping or slaving out to another amp as the isolated output can be set for different phase relationship, ground lift and cuts out the ground loop noise by isolation transformer. Works great on the front end of an amp to run two amps in parallel (no noise especially when one amp is in standby when you are turning on the amps). I tried using the Line6 DL4 to run two amps and that was noisy at best. I burned some circuits in it when I tried a solid state amp and tube amp together ( I was able to repair it after the damage though with a jumper wire to replace the vaporized copper traces). Never mix a tube amp and solid state amp by plugging in a parallel output into the input of each amp since the ground loop and associated voltage levels may not be compatible with each other. Something may go on you, also you may possibly have a more serious issue if you or your guitar become the short circuit to earth ground. Best to use a splitter that has an isolation transformer with a ground disconnect. I doubt there would be issue of concern for electric shock but there is that potential. Also it is noisy unless you can isolate one amp from the other. I am only providing reference to some product but I am not endorsing them. Just trying to be helpful and what worked for me.