The problem with parallel is that, even based on nominal impedance, you are looking a 2.4 ohms; much lower than that probably at minimum impedances; and what if minimums of the two speaker coincide?
Greenhorn question: Beware!
Is a 4 ohm exciter speaker and a 6 ohm woofer box, wired in series (total 10 ohm) connected to an 8 ohm output amp OK?