The sound of this product has been reviewed enough. I just wanted to say that, these retail for about $470 in China. Even if the seller got them at retail price, add $20 for shipping and stuff, they are still making over $200 per unit. This is just a rip off.
Also, the C4 should be paired up with headphones. Sensitive IEMs still sound decent, but really the C4 is designed to drive big cans really really well.