Hififorless(which doesn't even list senn cans on their site) is selling 580's and 590's now for buyitnow $150 on ebay.
And as to the "Ebay is now more than retail" thing - it was, but now it has stabilized, in addition to starting to define, at the after-market price to the retail price. Headphones are a small market, and easy to overlook/not know a good price for, which is why I was able to get the DT770's for $80. Many have anecdotes of great deals off ebay, but the majority on ebay is usually a little under retail, just like retail is usually a little under MSRP. It has become, for all intensive purposes, the "online mall" that everyone envisioned becoming the standard 4-8 years ago, and that failed utterly at the time. You will probably find many more permanent reseller items, at near-retail prices on ebay now than small incidentals that people found in their closets.