I hate to say it but BOSE IEM SUCK. No, let me rephrase that: ALL BOSE suck. You are buying brand name over quality with washed out sound. Tried them, sent them back.
You have a great player with enough power to drive some pretty good cans (I love Cowon!), so unless you are an audiophile an external amp is not really needed.
IF you want the BEST (and can afford them) it comes down to the Westone U3 or Shure 5x series. I prefer U3 myself BUT that is only a personal pref. Both are triple drivers for great reproduction of sound. Westone's are just more comfortable.
In the mid end Westone UM2s are hard to beat. A UM2 + Shure "Olive" foamies = kick ass listening experience. UE Super Fi 10s are VERY decent too...but are not my cup of tea thus the mid teir rating from me, even though they are a tripple drive IEM.
In the lower end Westone UM1s are very good. Shure's low end is MEH. Ultimate Ear Super Fi's 5 Pro's are very good for the price...IF they fit. They are on the large side...and stick out.
IF you are into HEAVEY Bass the Super Fi. 5 EBs will blow your mind with the amount of bass they deliver.
I usually buy my gear at
Earphone Solutions - Shure Earphones, Sennheiser Earbud, Ultimate Ears Ear Buds, Shure earbuds and Westone Earphones - The Best Earphones for iPod Comparisons and Reviews good peeps with great customer service.
YMMV, but the biggest suggestion I can make BESIDES try the dif brands before you buy. Is Garbage In Garbage Out. No sense owning U3s if you play 192 mp3's! With the high end IEMS they amplify the experience amazingly well IF the quality is there....if not they will make it sound HORRIBLE! Mid grade are more all round, and super high quality music is not as important. With the low end, some low bitrate music (especially heavy bass on the EBs) will sound BETTER on them than on a IEM costing 5x more!
YMMV but thats my recommendations. ;)
EDIT:
Never did like Emotic IEMS. Tried them and wasn't happy with the fit. That being said I do like their triple flange, mod'ed to a dual ;)