Lumos, is the ma900 basically a refined version of the same sound sig? Thats what it looks like looking at the measurements but since you have owned the ma900s yourself, maybe you can comment on this.
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Sorry for late response. To tell the truth I never compared them side by side and it was quite while ago so can't remember well enough. However Yes! same kind of Sony's engaging sound (upper-mids) and MA100's soundstage was WOW, never expected. Remember I was listening Karajan's 9th symphony one night with them and they performed indeed very well. Those times my best can was HD558, no Amp or Dac

Whose ringing was annoying though.   

So the ringing part that you confirmed to be annoying on the ma100 is totally absent on the ma900? Thats all i really need to know

Yes absolutely no ringing or any kind of odd distortion on MA900. Only issue I had with MA900 was their kinda fat bass, probably lots of D2 distortion. otherwise very nice engaging upper-mids

and I just got some MA300 to keep me from dying using apple ear buds, just needed something comfy for a bit using with my computer.
I quite like them. for 30 or however much they are... really not bad. comfort is great.

tonality is pretty okay, has a bit of U shaped but not a lot. maybe V and U at the same time actually? it's not bad at all. was hoping they would be a bit bass lighter though, might take me a while to get used to the bass amount. in games it's a bit harder to pick up positions of sounds due to bass being a bit overwhelming sometimes. might try EQ when gaming. the rest is actually rather neat for the price.
bad write-up but simply put: thumbs up, minor nitpicks: bassy and some dip in upper mids and some slight treble peak (not too bad IMO)