\[\left( \frac{a - 8^{\backslash a - 8}}{a + 8} - \frac{a + 8^{\backslash a + 8}}{a - 8} \right)\ :\frac{16a}{64 - a^{2}} =\]
\[= \frac{a^{2} - 16a + 64 - a^{2} - 16a - 64}{(a + 8)(a - 8)} \cdot \frac{64 - a^{2}}{16a} =\]
\[= \frac{- 32a \cdot (64 - a^{2})}{\left( a^{2} - 64 \right) \cdot 16a} = 2.\]