I'm not sure if it is paired with the 6D for a kit, but I'd look at the 24-70 f/4 IS instead of the 24-105. The 24-105 is a great focal range, but I never found it to be that sharp compared to my other L's and I wasn't a fan of the distortion at the wide end (although that is pretty easy to correct in post). The 24-70 f/4 is supposed to be much sharper, still has an f/4 aperture (if that fits your needs) and still has IS. on top of that, your 70-200 will cover the longer focal lengths. Personally I ditched the 24-105 for the 24-70 2.8 II, and while I sometimes miss the IS, I love the noticeable gain in sharpness (even if my wallet got a lot lighter).
With regards to zooms and primes:
Primes will be sharper than zooms at the same focal length most every time (although at smaller apertures, most zooms will sharpen up pretty good). The main reason I like primes is the wider aperture-- which is great for bokeh and thin DoF-- but I really love the fact that I can shoot in low light without cranking my ISO through the roof.
If you're always finding yourself shooting at f/4-f/8, then primes won't gain you a whole lot. They're physically lighter, but if you can't find a use for their low-light capabilities or take advantage of the wide aperture to throw the background out of focus, you might as well stick with your zooms for the flexibility.