$\frac{2^{3x}+\frac{1}{2^{3x}}}{(2^x+2^{-x})^2} .\frac{2^x-2^{-x}}{2^x+2^{-x}}$
$=\frac{2^{2x}.(2^{6x}+1)}{2^{3x}(2^{2x}+1)^2} .\frac{2^{2x}-1}{2^{2x}+1}$
$=\frac{(2^{2x}+1)(2^{4x}-2^{2x}+1)}{2^x(2^{2x}+1)^2} .\frac{2^{2x}-1}{2^{2x}+1}$
$=\frac{(2^{4x}-2^{2x}+1)}{2^x(2^{2x}+1)^2} .(2^{2x}-1)$