Hi again agentfox,
The 4-ohm specification is simply a result of running six drivers in parallel. With all those six voice coils in parallel in a multi-driver speaker, it's electrically impossible to get the impedance any higher than 4 ohms without imposing power-wasting resistors in the crossover circuits or making other design compromises.
And if you examine the impedance curve of the M80, it only touches 4 ohms over a fairly limited range in the bass. Nevertheless, it's still a nominally "4-ohm" speaker, and as such it presents challenges to amplifiers or receivers that can't deliver substantial amounts of current from their power supplies when called upon, which is why Axiom only recommends a few brands of AV receivers that will drive the M80s without shutting down or current limiting.
Regards,
