Jamie,
I don't mean any disrespect by this, but wouldn't installing a Magnaflow DI/DO muffler behind a X-pipe be a bit redundant? Those mufflers have a common central chamber, wherein the exhaust pulses can equalize in much the same way as a X-pipe.
On the Magnaflow website, the 5x11 oval mufflers with part numbers #12568 and #14568 (satin and polished stainless, respectively) are advertised as having a "Tru-X Perforated Core" which is essentially an internal X-pipe. The 4x9 oval mufflers are not advertised as having this feature, though they may anyway.
Just hoping to save someone a little $$....