I have both. I thought MG7 would be better for what I've read about it's bass. What I thought by reading: Plenty of bass, great impact, but very controlled - quality bass with much impact and little or no midbass. What I got: Very good and detailed bass with almost no midbass, not much impact. Bass is detailed but far from the rest of frequencies, not upfront, but detached, not connected to the rest. It's strange initially but you get used to it. Tips don't change the sound much on MG7 for me, it's just a matter of comfort.
I prefer Eternas (w biflanges) over MG7 for impact purely. I prefer TF10 (with foams) over MG7 for impact and quality os bass.
FXT90 and MG7 are on par for the bass. Impact is even, quality and control are best on MG7 but on FXT90 the bass is part of the music, not detached from it. FXT90 is brighter overall. Treble is similar but you need to have in mind that the FXT90 is brighter. What makes the FXT90 better for my tastes is simply: Soundstage and Dynamics.
FXT90 is my favourite IEM right now because it's very dynamic and fun... everything is upfront, I dont miss anything, like I miss severely the mids on TF10 and the bass on B2.
Hope this helps... even if it's a little (ok, very) confuse. o.O
