Fade, welcome, and be assured that it almost certainly has nothing to do with your receiver, and that no "upgrade" in that area is necessary. It's difficult to evaluate "oomph". There may be something in your calibration of the sub and speakers that needs adjusting, or has your previous experience made you expect some unnaturally heavy sound which the Axioms won't do when set properly? Experiment.

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Enjoy the music, not the equipment.