I'm not quite sure what you're saying here.
IEM = earphone that fits into your ear canal. IEMs use a sleeve or tip to provide a "seal" between your ear canal and the IEM. These sleeves are usually foam or silicon or rubber. The softness and flexibility of the sleeves allows the generic IEM to fit your unique ear canal. IEMs must be in the proper place to get the best quality of sound. If you don't get a good seal then the sound quality is poor. Also called canalphones.
Ear bud = earphones that sit inside the "bowl" of your ear. These phones do NOT seal themselves into your ear. They might have foam sleeve on the ouside to help them remain securely in your ear, but they aren't inserted into your ear canal. The stock phones that comes with the ipod are great examples of ear buds.
The logitech stealths you mentioned are actually IEMs.
There really isn't much you can do to make an IEM fit better. the fit is all in using the right kind of sleeve. The inside diameter of the sleeve has to fit the outside diameter of your IEM or else they slide off and don't seal properly. Not all IEMs are the same style, so what may fit one probably will not fit another. If you use the wrong sleeve, chances are you will leave the sleeve in your ear when you pull the IEM out or break the IEM trying to get the sleeve on.
I usually open my mouth, gently push the IEM into my ear canal, close my mouth and then enjoy the music. twisting while shoving is also a good technique.
You'll find a lot of high end IEMs have replaceable, interchangeable sleeves. These are the phones that usually start around $150 and go up in price. This isn't true 100% of the time, but its a good bet to make.
The lower end IEMs have sleeves exclusive to themselves. there are some threads about getting something to fit something it shouldn't, but those are the exceptions.
Hope this helps out a bit.
