Summary: Most of the magic from the KNS 8400 is retained in the KNS 6400 design. You get a rock solid set of headphones with a pleasing neutral sound signature. Some of the design changes hamper the performance somewhat, but even so they are still remarkably good value being priced at a mere $100.
Pros: Excellent price / performance ratio, Closed back design, Decent amount of noise attenuation, Comfortable to wear even over an extended period, User replaceable cable, Solid design, Good gaming performance, Excellent bundle
Cons: Not quite as efficient noise dampening as on the KNS 8400s, Cable is a bit too long for portable use