i'm not sure if you still have them but if you do try them with different eartips (i'm usually a medium and i found the stock biflanges on the hifiman re400s to sound similar to what your saying). if your getting sibilance from the re400s, its definitely an issue with the fit and seal. try the sony eartips from the sony earphones you have (odds are they are the sony hybrids) and they match very well with the re400s. but in the end they aren't bass monsters by any means just a slight lift in the midbass and a smooth treble. lemme know how it works!