The sub is an Mirage Omni S-10,
Trust me if it said Divinci I would have stayed away from it...
He didnt state it as "NEW" just a used once for a convention demo...
So technically this unit is used. Get hold of Mirage and see if there is warranty left on this unit, and if it transfers to you.
Was there any warranty offered, given or implied by the seller? Used merchandise purchased with no warranty offered by the seller is as is as was. However the seller said the unit was 10/10 so this could be interpreted as an implied warranty.
Unfortunately you are on much less certain ground than if you had purchased a new unit from a reputable dealer.
If I buy used, I assume I could be stuck, and have been, so I don't purchase anything, I don't feel competent to service.
Unfortunately that unit is almost certain to need a new amp and 10" driver. If Mirage can not help you out, for instance if warranty has expired since the demo, then you are at the mercy of the seller.
Try moving the driver cone in and out and see if you feel any rubbing, grating or grinding. If you do, it is certain the driver needs replacement. If not, you can replace the amp and see how it sounds. If it sounds like you described, but without the popping or any other problems then the driver will still need replacement. Also find out the correct DC resistance of the driver, and check it. After what you described there could be shorted turns on the voice coil, drastically dropping the impedance. If that has happened then you will blow the new amp and keep chasing your tail so to speak. I'm concerned, as from your description the woofer was very likely powered beyond its mechanical limits, by the violent popping.