couple quick things, there is no Injen fix for the 6i from cp-e, that's only for the 6s. IF the mazdaspeed part is the exact same as the AEM one, then you do chance a CEL, which there is no fix for. in most cases, a mazdaspeed part will not cause a CEL whatsoever, which is why i'd guess it's not the same as AEM.
the gains will be minimal, but there would be no more than 4hp difference between all of the intakes for the 6i....so just get what you want. so i'd recommend the mazdaspeed intake if it's already an option in your eyes.