I found that the OS100 matches well with the Delta too, it managed to reduce that 7-ish kHz peak so the treble is smoother now. I did find that transparency is slightly reduced, though could be an effect of the treble attenuation. And yea as @earfonia mentioned, the O1S00s don't affect the low end too much. Going to 200 and 300 though, the treble attenuation is supposed to increase, and the bass quantity as well.
Forgot to mention, thanks to you @RedTwilight who introduced and helped me to buy the Ostry eartips! Good buy!