Let's come to the Sound:
MIDS:
The main strength of this particular iem is the Mids. They are just a little bit forward. Although the instruments came forward, i find the vocals are somewhat laid back, just a little. But the vocals are a beauty when i try with some vocalcentric songs.
TREBLE :
Treble is quite good. I didn't find any sibilance. It has got a smooth treble without any compromise on details and resolution, that means you can have a long listening session without any fatigue.
BASS :
Here comes the twist, it has got a huge quantity of bass but lacks in quality. The low frequency are mostly focus on the Midbass. That is clearly due to the missing of Subbass. I didn't find those rumble and slams either. And one more thing the decay of the bass is somewhat longer than usual.
SOUNDSTAGE :
It has got a wide soundstage (above average). But it mainly focus on the width and not into the depth. The instrument seperation is quite good with enough width. You won't find any congestion.
Overall the Sennheiser ie 300 is a very smooth and fun sounding iem.