Hi,
The Ohms have nothing to do with the sound signature of your speaker; it is only a value indicating what resistance is the speaker offering to the amplifier. Alan has written an excellent article covering this topic -
Easy Answers to Confusing Specs: Sorting Out "Impedance" Your Axiom VP150 center speaker should be classified as "Small" in your initial Yamaha speaker configuration. Using a sound pressure level, verify the speaker volume level of your speakers if needed the center speaker can be increased by a few dBs more than your left and right main speakers. Try it without applying any corrections from the Auto EQ function of your yamaha; run your Axiom speakers flat.
Then if you still have the same issue, please, remove the grille off the speaker and verify if all the drivers are functioning.
Keep us posted !
