Several revisions to the 500v2 in the last 3 years, really? I know the amps took a little different shape and changed some of the wording/switches on the panel but it is essentialy the same sub it was when it came out, as far as I can tell.
The EP350v3 is a great sub it doesn't reach quite as low but only by a few hz difference. The EP500 does have a bit more power to it and it is a noticeable improvement in feel over the 350, IMO.
I am glad I don't have to make this decision.
I think if I could get the EP500 for a little less than the cost of the EP350v3 from the FO, I might be more inclined to get the 500.