@dfkt - Thanks. That clears up a lot. I've read some other comments that say the SM3s lower midrange seems boosted in comparison to the upper midrange, and what you're describing fits with what happens when I boost the lower midrange and bass of the PFE. The sound has more weight, but the upper mids and treble take a slight step back relative to the rest of the spectrum.
This isn't a bad thing as it actually makes the PFE a little more dynamic and more pleasant to listen to, especially at lower volumes. The sound just has more body.
I can now better understand what you mean when you said the SM3 treble takes a backseat to the mids and bass, but it's not rolled off or muffled.