It is purely up to what level of complexity you want to have. Wireless lan networks operate on preset channels. If you have one in you home, and you do not want this audio system to interfer with it, you would setup your wlan at one channel frequency, and set up the FSK audio link on another frequency channel. All would then be well. This is probably the best way for a hobbyist to set up such a system cheaply.
If, on the other hand, you are concerned about interfrerence with other wlan networks that you do not have control over, then the best way is to use some sort of spread spectrum system for the audio. It could still be fsk, but frequency hopped, and you would need to send the audio in packets. It could be some sort of 802.11 type modulation, using a standard chipset. There are some chipsets that can do a collision avoidance search of the rf spectrum, and pick a frequency channel that is not used too much.