Wow. I have quite a different opinion of the Plug vs. Etymotic (I'm assuming you mean the ER-6 or ER-6i). I found the Koss to be
extremely bass-heavy. While it could get the toes tapping and the head bopping, it was anything but neutral (okay, more like exagerrated/bloated). The fit was relatively easy, and they were comfy to wear.
The Ety's, by comparison, are quite neutral and much more detailed. The trick is definitely in the fit, though, as even a little difference in how good the seal is will affect the bass significantly. If the seal is a little loose, then the bass will admittedly be weak, but with a good seal, the bass won't be slamming, but it will be there. I've found the foam plugs to work the best - the silicone flanges bothered my ears and it was hard to get a consistently good fit. I do find the midrange a little dry, but the highs are extremely good and overall it's a much more balanced presentation than I got from the Plugs.
Plus the Ety's block out a little more sound (I believe), and every little bit counts when you're flying or in a noisy environment. I never go flying without my Ety's, they really do make a HUGE difference in flying fatigue.
Anyway, just thought I'd give my two bits. Although, given the price difference, if you're not going to be listening critically, go for the Plugs.
