Sir, just to share my early expiriences in hooking up a 4 ohms drivers to a 6 - 16 ohms mosfet power amp.
I used to have a mosfet power amp branded as LO-D model HMA-4590, it is rated at 6-16 ohms at 55W/ch, I used this to drive my low drivers, one time I accidentally hooked up a 4ohms 500W dual active crown woofers. without knowing it, after a few minutes in operation, my LO-D is literally in flames...
After learning from this mistakes, I make it a point to take a look at the drivers rating before hooking it up with the amp. my moto bacame "when in doubt check it out"...
Lesson 101 never put your amp in danger (specially the expensive ones) when your in doubt about the compatibility of your drivers (eg. impedance, sensitivity, power etc...) dont sacrifice by experimenting, if problem persist, consult a technician