IE7 has a much bigger soundstage, and much more neutral tone. Isolation is not as good as S4. Vocals are more forward and detailed. Very relaxed sound with plenty of detail.
S4 has the very bright Klipsch sound signature. Bass is not as controlled as the IE7. Highs are bright but seem very colored compared to the IE7. The S4 is a colored, "fun" IEM. The S4 is so bright you may cringe at sibilance if any of your music if your music was recorded with any. The S4 sounded like a low-cost driver that tried really really hard to sound like a higher end driver.
The S4 was also designed for consumers listening to MP3's and lower bitrate music with any source. The IE7 is less forgiving with lower bitrate music, but not too bad, nothing like a high-end monitor IEM.
Other than them both being dynamic IEM's with decent bass impact, they are very different IEM's.