theirs a 200w difference between those 2 amps @ 2ohm and about $65. with 200w, it wouldnt be a big difference.
i would go with bxi2006 to save yourself room to add additional sub and run it at 1ohm to get its full potential. if your not planning to upgrade and set on a single type-x, i would look into a solid 2-ohm stable amp (kicker and rockford fosgate comes to mind)
Id go with the 2006, like stated if you ever want to send more power to something can run the amp at 1ohm. It would pay off in the long run if you plan on switching subs out or whatnot.