I'll comment on a couple points. As to the efficiency, yes, this is sometimes not understood, and a "big speaker/big amplifier" mentality is in control. The reality is that the bigger speaker is often(though not always)more efficient than the smaller ones and actually uses less power. Your VSX-94TXH should easily power your Axioms to beyond safe listening levels.

As to the sub comparison, the first thought that comes to mind is whether the EP500 isn't as favorably located as was the VTF3 for optimum bass extension. Comparisons should be with all factors equal, to the extent possible. My own EP500 has excellent extension to about 17-18Hz. Another factor is that the EP500 may be correctly calibrated for a balanced level with the speakers, while the VTF3 was simply set too loud.
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Enjoy the music, not the equipment.