Lyne, I don't think those are P6 bugs. I've had the same problems with P5.

The hard edges are probably due to the extreme pose. It's hard-looking because the hair is passing through the figure. There should be morphs that let you fix that sort of thing. If not, slight scaling should do it.

Visible skullcaps are a common problem with Koz's and 3Dream's hair in P5. First, make sure the transparency settings are right. Transparency should be 1, Transparency edge should 1, Transparency falloff should be zero.

If that's not it, try rendering with shadows off. If that fixes it, the problem is the shadow of either the hair or the skullcap. Make sure cast shadows is off for the skullcap. If it's the hair that's casting weird shadows, increase the size of your shadow depth map until the shadows look right.

As for the hair textures...do not use texture filtering. Instead, click on the hair and decrease the shading rate to at least 0.05. (I use 0.02, usually, but that will render very slowly.) Usually, the neck part of the hair is the only part you have to adjust. Then in render settings, lower the shading rate to match the shading rate of the hair.

FWIW, the Egypt Hair rendered great for me, right out of the box. But IMO, that's how it is with both P5 and P6. The transparency settings can be kind of random when the product was made for P4.