The K10 and the 6 are a bit different tuning. The best I can describe it is that the 6 is the 4 + bass (just to give you an impression, as you said you have the 4). The 4, to my ears, is fairly bass light. It's detailed and accurate, but it just lacks the extra "oomph" that the K10 provides. I've long held that the 4 is the "K10-lite", as they have fairly similar mostly-neutral tunings.
The best thing about the K10 is that it doesn't emphasize any one part of the spectrum, but it certainly has the power to provide in any particular area where it's called for. If there's a big bass slam, you'll feel it, but if it's not in the recording it's not going to be added. The 4, on the other hand, has very polite bass -- it's there, but it's definitely not overpowering, and it doesn't steal the show.
As I said, the 6 is basically the 4 + extra bass. It is slightly bass-emphasized compared with the K10. I would go so far as to call the 6 a more "fun" sound -- it takes a little bit of liberty with the recording, adding a little bit of extra energy and impact. The K10 stays very true to the recording -- it can definitely be fun if the recording is mixed that way, but it won't take any liberties and will be one of the most transparent headphones I've ever heard.
So, the K10 and the 6 don't really try to be the same thing, and that is very good. The extra bass drivers allow the other drivers in the 6 to be a bit more detailed, and the bass doesn't bleed into the mids or the highs. It is still very detailed, but the bass is definitely the star of the show. I would actually compare the 6 more to the Shure SE846 than I would to the K10, although again I think that the 6 is just ever so slightly more to my tastes than the SE846 -- they share the same slightly elevated bass and excellent mids and highs.
If you would like extra baseline bass, the 6 will give you even more than the K10. The 6 is great for its more fun signature. It is engaging, and it livens up the music. However, if you just want to hear the music and don't want to hear the headphone, you're still going to reach for the K10.
Hope that helps!
Edited by sq3rjick - 10/21/14 at 8:03am