If your N5 and desktop are on the same subnet, you can control and listen to iTunes, even though the desktop is not on the wireless. My home system is like that (the primary desktop mac is a wired ethernet into my LAN and has its wifi card turned off).
In order for your N5 (any wifi client) to work this way requires your wireless (wifi) router to be in access point mode (which is NOT the default), not in normal router mode. How easy this is to do depends entirely on your particular wifi router, and your skill at configuring it.
(When your N5 and desktop are on the same subnet, you can use AirBubble on your N5 to receive the audio from iTunes on your desktop machine, and you can use Remote for iTunes to control the running iTunes on your desktop. Works very well).