i also have a pair of DT-50's which with 2.0 really DO sound exceptional. But, back to topic.
I have a helix and have only connected it to the 2 dt'S via Analog connection. Trying the typical (and NOT so typical) Helix Stereo Send (pre of the amp models of course) to the front of each DT50,,which, realistically as much as you're gonna' hate to hear it-gives the best sound IF YOU SELECT THE RIGHT PRE EFFECTS.
WHen I tried to go to STEP 2 {aka} bringing the DT50's SEND back INTO the HELIX STEREO (one DT50 per side L and R) Return to POST effect processing ie. Delay, Reverb, Cabinet IRs, etc. and then take a another set of SENDS panned L and R and placed at the very end of the line, and sent those to each DT50's effect RETURN, and then letting it go into the TUBE section and then out to each DT50's 4x12 Cabinet. IT WORKED...BUT...it became very difficult to get gains throught the Helix set to a POINT that didn't cause TOO much noise (even with noise gate right before the Helix's final OUTPUT) and the other end of the spectrum was squealing from too much gain going into the Power amp Buffer stage.
Oh, and by the way, if you're curious why I used a set of SENDS to go out to the DT50s instead of the Helix's Main outs? I suggest YOU try that for yourself. You will NOT be happy.