I think if you go parallel you create
a 16 OHM load. Series will drop you to
4 Ohms (or possible less if you speakers are not exactly labled. Danger is, if your speakers transiently drop to a very low
rating it is possible that you will release
blue smoke from your amplifier or speaker. As you know it is incredibly important to keep the blue smoke INSIDE the boxes. To wire in series you wire red to the first speaker and bridge from....Wait...Just go parallel.

Eddyboy