This will be fun! But it's a shame I could have saved you 200€ by writing your review for you. "The ER4S is lacking any semblance of bass. The soundstage is claustrophobically small. And as for the fit, I might as well be jamming pencils in my ears; they might even sound nicer."
And the red filters are recommended. There is plenty of info here, including where to buy them and graphs from Rin. The effect is rather minimal, but the reds bring down the mids and some upper treble about 2dB. This sounds more accurate to me and lusident.
And don't forget the horrible cable noise every time you move! ;-) haha
The red's are subtle but after listening to them a while they really make things a little bit more easy to listen to in the sense that they take down the one or two trouble areas of the treble. By trouble areas I just mean they improve what isn't as perfect. Related to other earphones the stock filters sound amazing. ;)