Our DS-6500 (bought in 2015) only has USB. The manual says something about an optional network module, but I don't know if this is available to buy.
The DS-6500N has a built-in Ethernet connection, but is also 50% more expensive, which in my opinion is overpaying.
As soon as a USB connection is used, the unit can no longer be accessed via the network. Accordingly, it unfortunately only works with one type of connection.