I've been following this thread for a while and something is amiss here. Some thoughts:
Axiom should have done more testing instead of rushing out the new models
The EP500 is not a new design. It has been around for several years now. Its true that they have made some changes, but those are relatively minor. The sub works very well for a number of people here so I think you can eliminate design as an issue.
That leaves the following:
1. Poor room acoustically. The experts you have coming should be able to measure this. If they can't they're not experts. If you have big nulls in your room somewhere in the 40-200Hz region (yes, thats above what your sub produces) it can have a big impact on your bass.
2. Expectations different from how Axiom designed their subs to sound. Axiom is obsessed with reproducing exactly what is in the originally recorded material. Maybe you are used to an 'older style' sound where some frequencies are over emphasized. Getting an inexpensive equalizer for your sub so you can boost some of the frequencies to see if that improves what you hear.
3. The sub is broken. Axiom builds quality stuff, but nobody is perfect and when you ship large heavy objects by courier the get knocked about a fair bit.
Since you have arranged for the experts to come out, wait for them to show up to see what they have to say. I would actually call them to confirm that they will measure in room response of your mains and your sub. If they won't, they are not worth having out to your place.
Another thought. See if your experts can bring something to do a test EQ of your sub to see if they can change the in room response to something more to your liking.
