That stuff from the factory outlet is $1,407. The price for four-year-old gear should be less than that.
But how much less depends on many other factors that none of us can help with. Condition of the speakers, the overall willingness to sell, the level of friendship, etc.
The 'correct' price is the price that the buyer and seller agree to. Nothing more, nothing less.
If you really need some sort of 'blue book value' for the speakers, about the only thing you can do is to search eBay or Craigslist. Though Axiom speakers are pretty hard to come across on the used market (which should tell you someting
). You may not find much to go on.
I agree with the others though. Perhaps your friend should tell his wife that he's thinking of trading her in on a smaller model too.
PS: Do tread carefully with this thread. Axiom is very tolerant when it comes to what we can discuss here. But one thing they really frown upon are 'for-sale ads'. I'm not saying that's happening here, but just a warning for where this
might be headed.