hey guys i am in the same boat as the OP. like the OP i like my bass deep and with good impact, quantity, and extension but not over the top (sony XB500) or headache inducing. i came very close to getting the beats by dr dre studio because of its bass, but ended up with the denon D1001 instead. they are still currently my favourite headphones of all time.
ever since i got the denons i wanted a pair of IEMs that could at least come close to the bass of the D1001s, but i have still not found them yet. the closest i have gotten are the sennheiser IE8s, but even with the bass dial on max they are not enough for me. also the lack of isolation annoys me some as well.
so my next pair will either be the MTP golds or the JVC FX500s. a lot of people rave about the FX500s and its bass. but i am unsure which to try first, considering i could save a fair bit of $ getting the JVCs first instead of the monsters.
for the OP, i would not recommend the shures or the westones. i have personally tried the se530s/westone 3s/UM2s (still own 530s/UM2s) and none of them do it for me in the bass department.
the shures have almost zero bass, and i only use them when i want to hear better vocals.
as for the westones, before i bought my UM2s a year ago i did some serious research into both the UM2s and westone 3s. i even found a audiologist with both IEMs on site for testing, and went out of my way to go listen to them. the first time i A/B'ed listening unamped out of my sansa clip, they sounded very similar in sound signature. the UM2s were more revealing and flat-ish, which makes sense because the UM series are monitors for musicians. looking back at my raw listening notes, i found the westone 3's bass to be slightly boomier, almost slightly hollow as if it lacked some weight. btw this was done with the yellow foam ear tips, in a completely quiet environment.
almost a year later i tried A/B-ing them again, same place but my own pair of UM2s, listening to my ipod LOD out amped with a minibox E+. what was scary was the longer i listened, the more similar the bass sounded to me. although i still found the UM2s to be more revealing, almost more natural sounding.
after getting the monster turbines (vanilla = original models) and the IE8s, i concluded that (for the most part) balanced armatures in universals will have a harder time matching or coming close to the bass capabilities of dynamics. i say for the most part because there are exceptions like the custom molds from JH audio/UE/Westone etc.
and to get an idea of my demands for bass, some of my favourite songs include:
pyromania - Cascada
a never ending dream - Cascada
keep you much longer - akon
always be my baby - mariah carey