8. Let $\left\{a_{n}\right\}$ be an arithmetic sequence with the sum of the first $n$ terms denoted as $S_{n}$. It is known that $\left(a_{6}-1\right)^{3}+2013\left(a_{6}-1\right)^{3}=1$, $\left(a_{2008}-1\right)^{3}=2013\left(a_{2008}-1\right)^{3}=-1$, then which of the following conclusions is correct?
A. $S_{2013}=2013, a_{2008}a_{6}$
C. $S_{2013}=-2013, a_{2008} \leqslant a_{6}$
D. $S_{2013}=-2013, a_{2008} \geqslant a_{6}$
$$
a_{6}-1=1-a_{2008} \Rightarrow a_{1}+a_{2013}=a_{6}+a_{2008}=2 \Rightarrow S_{2013}=2013 \text {, }
$$

Obviously $a_{6}-1>0 \Rightarrow a_{6}>1>a_{2008}$, so the answer is $A$.