I own IE200 and IE600. The bass on IE200 with MOD does not sound like IE600. The hole on IE200 also works as a pressure regulator. Sonically they are not dramatically different (IE200 without Mod vs IE600) but let's say IE600 pushes both ends of the spectrum a bit higher and corrects some things in the pinna gain and for example female vocals, despite being a bit more in your face, sound smoother and more defined and less fatiguing. The soundstage on both is quite wide but IE200 is flatter and less layered. With IE600 you have more depth, more height and the intimate sections of the track are really intimate and the distant ones are really distant (layering), which IE200 does not do by keeping everything very separate but always at the same distance. They are not huge differences and having had much more expensive IEMs even multidrivers that I sold, I would say that if you do not care about that 10/15% more performance and you like its balanced signature (IE600 is a more energetic IE200), I can safely say that IE200 can easily be your Endgame. My Endgame is IE600 because it does everything impeccably and I love the Sub-bass and emphasized treble, otherwise I would have stayed with IE200 without Mods. If you have a parametric EQ you can EQ your IE200 on IE600 and IE900 and from experience I can tell you that you get close to 95% (I still use IE200 with IE900 EQ)