It's annoying farming demonic essences but I can say in the long run it's well worth it! Try lower MP's for that in act1 if you want speed, or if boredom doesn't kill you, there's good ol' Warrior's Rest runs on mp8-10. Best of luck.
I tried DE farming COTA runs instead of VOTA runs to break up the monotony. COTA drop rate sucked bad for me though. Guess there's a substantial difference when farming COTA at higher MP levels. I just did it on MP5 like I do VOTA so I could kill in 1-3 bells. Dunno why the drop rate was so bad. I did both for an hour each and in VOTA I got like 20-25ish DE's in an hour, but in COTA I got like 11 or 13 or something like that after an hour.
Maybe I should do WR and COTA in the same run and see if my results are better. Or maybe swap to DW setup and farm a higher MP.