Duel against Sennheiser IE8 : bass quantity is the same but bass is tighter on the Yamahas, mids and treble are much more clear on the Yamahas, soundstage is better on the Sennheisers (IE8 puts you in the middle of a theater, while EPH-100 are placing you in the middle of the living room), instrument separation is so much better on the Yamahas than the Sennheisers sound muddy, although they're not especially. Isolation is better on the Yamahas. Except for classical music where soundstage really helps the IE8, these Yamahas differ from IE8s in every possible way. Winner: Yamahas.
Duel against JVC HA-FX700 : bass has a similar tightness but is more reasonable on the Yamahas (not for bassheads), mids are more forward on the Yamahas, treble are more forward on the JVCs, so JVCs remain better for female voices and high-pitch percussions, but Yamahas win for metal and progressive rock. Instrument separation is a better on Yamahas, soundstage is significantly better for Yamahas (the band is sitting around you), clarity is slightly better on Yamahas. It's a draw in my opinion, I'd say they're complementary.
Duel against Shure SE420 : bass is better on Yamahas (stronger, tighter), mids and treble are similar quantity-wise, instrument separation is slightly better with Yamahas, clarity is way better with Yamahas. Isolation is slightly better with Shures but not by much. Overall, a clear win for Yamahas with all music styles, I'm definitely not a big fan of armature-type IEMs. Winner: Yamahas.
Duel against Westone UM3X : overall image is the same, good bass, forward mids, fine treble, excellent separation and clarity for both. Soundstage is smaller with the Westone, bass are more punchy on the Yamahas but equal in quantity, and overall Westone are more on the soft side (some would say "natural") whereas Yamahas are a bit more sparkling (some would say "lively" without causing fatigue). It's a draw in my opinion, I'd say they have a similar overall image (in one word: CLEAN) but you can still guess which one is dynamic-type and which one is armature-based.