Assuming its a Kicker ZX, because iirc the KX series was a 600.1 not 750, its only 2 ohm stable. Which means youre kinda fucked. You can either run your amp at 4 ohms with both subs, or ditch one sub and run 750 watts to just one, both being somewhat shitty options. Best options being to return the subs for dual 2 ohm ones, or get a 1 ohm stable amp.