A Network Player (or any standard UPnP client), does not interface directly with iTunes. It can, however, play music stored within your iTunes Media Folder.
This folder is where iTunes stores your downloaded content and you will need a UPnP media server to access this information via your Network Player.
Please note; any playlists or album art that are created in iTunes will not be available to the Player, as iTunes itself creates these and stores them in its own directories.
In order to view album art and other track information, this must be stored in the music file's own metadata - iTunes does not do this for you. There are many tagging programs available (for example Media Monkey or dBpoweramp), which can do this. Please see our FAQ on the necessity of metadata tags here.