RE400 - most neutral with a mild mid-bass lift. Upper midrange sounded a little off for me. Good detail.
S2 - bass reaches lower than 400 with less mid-bass. Good mids and treble can be a little hot at louder volumes. Not sibilant though. Overall more fun sounding as 400 with just as good details.
MA750 - biggest bass with nice combination of sub and mid-bass. Very smooth, forward midrange. Treble sounds less aggressive as the other two but retains nice clarity. Nice staging and just as big as S2 if not bigger.