Asking price seems fair to me as well being that the speakers are custom made and can only be obtained either via Jim himself at full price or via a previous owner as in this case. When you factor in that you might have to wait a few weeks to get a brand new set, this certainly doesn't seem like a bad deal at all.
To me it doesn't matter if you paid $1,600 for them originally compared to what they go for now. It's supply and demand and if the demand is not there then the seller can lower his asking price. Nothing out there says that you can only get x percentage of what you paid for an item new when you sell it on the used market.
I'm sure like most Salk speakers on the used market, they will sell relatively quickly.
Good luck on the sale!