So I have an M-Audio USB recording interface which can also be used as a sound-outputting device (which I regularly use when I'm using my laptop since the on-board soundcard sucks and creates an audible hiss on any listening device I plug into it) and I've tested a few doses using my old Fen-Tone DR-75-C's purchased from a thrift store as well as through my Hippo VB earbuds. Listening to normal music I use my headphones over my earbuds at such a volume that they act as if I had dual drivers. However, I notice that there is slight reverb due to the air chamber between the two drivers so I decided having stacked phones were useless for I-Dosing.
In the end, though my headphones lack sparkling highs and have a mediocre mids compared to my earbuds, I seem to get stronger reactions (if any) through my cans in comparison to the small earbuds.
Furthermore, it seems that higher quality sound equipment can aid in getting more out of a dose. Nights where I plug straight into my laptop's on-board soundcard and lay in bed, though I get effects from some doses, they don't seem very powerful.
Then again, that's just me. Anyone else find similar observations?