I found that taking MXE whilst on opiates brings on a much heavier nod. The time I tried MXE (20mg) with O-DT, I actually fell asleep (something that I can never do on opiates, therefore I wonder if 'passed out' is a better term), and woke up in a state of bad confusion and very short of breath. I also had a thumping headache that lasted the rest of the night and the next day. I don't want to jump to conclusions, but I am aware of the symptoms of opiate overdose when I see them. I'm pretty sure it was the MXE that caused this, since I wasn't on an exactly heroic dose of O-DT.
So my advice would be to tread carefully. Obviously a very strong nod feels amazing, but don't take much MXE at all. Definitely don't try to M-Hole while you're on the nod.