How to symbolically integrate a function of 6 variables?

I have a big function of 6 variables in total – x1, x11, x2, x22, x3, x33.

f6[x1_, x2_, x3_, x11_, x22_, x33_] := -((
3 (4 (x1 - x11)^2 - (x2 - x22)^2 - (x3 - x33)^2) ((x2 - 
x22)^2 + (x3 - x33)^2))/(
8 [Pi] ((x1 - x11)^2 + (x2 - x22)^2 + (x3 - x33)^2)^(7/2)));

I need to use indefinite integral because i need to get a symbolic expression.

I am using Wolfram Mathematica 7.

I tried something very simple:

FullSimplify@
Integrate[f6[x1, x2, x3, x11, x22, x33], x1, x2, x3, x11, x22, x33]

I waited for about 30 minutes and nothing happened.
It is obviously a complicated integral.

Can anyone tell me how to solve this problem?
Is there a way to simplify the function so the integration is easier for Mathematica?

Integrate[f6[x1, x2, x3, x11, x22, x33], x1 , x11, x2, x22, x3, x33]