If \(\displaystyle I = \int_{0}^{\frac{\pi}{2}} \frac{\sin^{\frac{3}{2}} x}{\sin^{\frac{3}{2}} x + \cos^{\frac{3}{2}} x} \, dx \) then \(\displaystyle \int_{0}^{2I} \frac{x \sin x \cos x}{\sin^{4} x + \cos^{4} x} \, dx \) equals:
\( \frac{\pi^{2}}{4} \)
\( \frac{\pi^{2}}{12} \)
\( \frac{\pi^{2}}{16} \)
\( \frac{\pi^{2}}{8} \)