When you parallel or series speakers, you create a different impedance. Series up (2) 8 ohm speakers, you've created (electronically) a 16 ohm speaker. Parallel em, you get a 4 ohm speaker.
Go too low on the impedance, you may hurt the amp due to increased power draw.
Go too high, you lose power.
Will 16 ohms hurt the amp? Probably not at these power levels. I'd try wiring them in series first.
Heck, I don't even know what the original speakers impedance is.