Out of your sig, I have only used the IE8 and SE530. I wouldn't relate the Custom 3 like either of them. The Custom 3 sound is more closely linked to a Westone product or ER4 where the notes are more on the thicker, textured side of BA drivers.
A copy/paste of what I've written elsewhere:
Klipsch Custom 3
Bass: robust, thick, with a real sense of authority, slightly dominant emphasis
Mid: thick and warm, the lower end is presented more robustly, smooth, slightly dark/veiled
Treble: good sensitivity that is well extended, slightly laid back in presence, slightly smooth, retains a good amount of detail
Stage: spacious presence with a significant perceived depth, roomy and layered, yet not far away
Location: ok sense of location but somewhat blurred, not exact
Clarity: thick and full bodied, lacks some crispness and articulation of note favoring a smoother, thicker presentation, sounds tend to blend slightly together but not badly, can come across slightly muffled at times
Tone: strong lower frequency emphasis with some countering by a slight treble bump in sensitivity, very balanced sounding across the board, decently natural and balanced.
Dynamics: excellent dynamic energy, strong, authoritative, some explosiveness and sense of energy, good linearity, lacks subtlety of notes due to the thick note presentation
The Custom 3 is a robust and energetic earphone. It offers a thick, powerful sound, and a great frequency response balance right out of the box. The sound stage is nicely sized and spacious with good separation and distancing. The only gripes would be that the thickness and smoothness of note does hide finer details and the physical cabling of the earphone is terrible.
Comments on the response:
While the frequency response isn't flat, it's likable and I feel specifically done for the intent Klipsch had for the earphone. I really like the drivers used. I think they were chosen smartly and function very well. Don't be fooled by the bass roll off too much. The driver itself is actually quite good at low frequency reproduction, better than most BA drivers, and it will get you whatever you want with some EQing. The treble driver matches the bass driver's sound. It does fall a little short on the top end, not bad but other high frequency drivers offer more top end. The crossover is well done, and the blending sounds seemless. Even though there's a midrange dip, EQing is very effective at flattening it out if desired (unlike some multi-driver BA earphones where there seem to be phase issues associated with the dip). One of the bigger benefits of the Custom 3 is the sound stage. It is well and naturally sized, can portray both proximity and distance, and is relatively linear in spacing.