I also feel I'm suffering from pretty low transfer speeds
Any concrete data?? How slow is 'pretty low'??
when you say that you 'changed the switch', what does that mean?
Nothing to do with the NAS as such, the switch in this context is a network switch (a device that routes data from one directly attached device to another). Many home networks don't use switches but instead may have a network hub (which serves the same purpose as a switch, but broadcasts any data to all directly attached devices, and becomes considerably less effective as the number of directly attached devices increases) or a router of some description (which can route data to different networks and will normally be connected to both the Internet and the local network in a SOHO type environment). These days many home setups just have a broadband router which, in addition to connecting to the outside world and providing a handful of wired network ports, will also have a wireless capability.
Bottom line is that the original problem was nothing to do with the DNS323 but instead was probably a fault in the network switch (a Netgear GS605, as per the OP).
Moral of the tale is probably that selling NAS devices as something that you can simply plug in and get working well without any technical knowledge of networking is probably a little optimistic and no doubt results in a significant percentage of the support requests for these kinds of devices.