Same here. I used the SE215's (for a while) when I had my PSM200.
I've since learned that single driver buds - since they have to reproduce the entire spectrum and have inherent mechanical inefficiencies - tend to cause ear fatigue more quickly than multi-driver buds. When that happens, one tends to turn them up to hear better, which in turn causes more fatigue. Vicious cycle.
Think of using only one speaker for your PA.. similar issues with maintaining definition, separation and clarity. Plus, that single driver works hard!
Have long since moved to 4, then 8-driver buds!