The HF3 has a very mid-centric sound that is very clean, detailed and unveiled, the highs are clearly present and clean as well but only go up to 15KHz which I believe is deliberate by the manufacturer. The bass is present but is definitely on the light side and only goes down to 20hz.
Based on your review I am pretty sure the ES5 would bring a massive smile to my face just because of the mids and highs and if the bass is more impactful then I will really be happy.
But I won't be able to afford these for a good long while which will allow me to try out some custom tips on my HF3 to see how I like custom tips.
Custom tips may make you like your HF3's a bit more because it will help create a more secure fit. As a result, the sonic transfer from the speakers to your ears wont be hindered by a less than stellar fit. Good luck!
Edited by Tronz - 12/28/11 at 6:14pm