PS Audio sold many Direct Stream units and as I recall there was a long waiting list.
Because so many units were sold, the more will eventually show up on the used market.
I also think PS sells their units at the initial prices to recoup there research and development cost.
Once that is complete, they start marking them down in price. However, that is just my opinion.
The firmware upgrades have been significant, and more are sure to come.
I will say this about PS Audio they do stand behind there products. I had a P10 power fail due to something I did, and they still fixed it for no charge.
With my Direct stream, I am using a iFi micro–USBPower and a iFi Purifier conditioner. Both of these items improve the sound quality and are relatively inexpensive.