Dom,
I can not say for sure you can't get the resonator separately however, I've been all through the Mflow catalog and there are no mufflers with as long and narrow a case as this and with the pipe centerline spacing as close with 3" inlet/outlets.
As for the internal x-pipe I saw that for myself. One of the installers commented on it as well. I suspect the double x-pipe combination is engineered that way for a reason, probably to control the resonance.
H
