The Soundmagic E10C is an Inner Ear Monitor (IEM)
The Koss KSC-75 is a supra aural headphone, albeit with ear clips instead of a headband.
You will find that asking questions about sound quality differences between two totally different type of headphones is fruitless. The KSC-75 is less than $15. Why not just buy a pair? That's probably the easiest way to answer your question. In the meantime, I can tell you that the KSC-75 has no equal in its price-performance range. Unlike IEMs, you will find that the supra aural style with ear clips means that pressure fits with the ear are not critical to maintaining great, thumping bass. Meanwhile, besides that thumping bass, the KSC-75 midrange is pretty good and it provides enough sparkle and detail to make you feel like you're listening to a high-end headphone.
Anyone who is interested in headphones should have a pair of KSC-75s, period. The only down side I can think of is the horribly tasteless silver finish. However, Massdrop has addressed that with their current offering of all-black KSC-75s for only a couple dollars more than that $15 cited above.