There are plenty of ways to get audio from your Mac to your HiFi. AirPlay works great, if you have an AirPlay friendly system or an Apple TV.
If you want to do it on the cheap, check out WiFi2HiFi, which we've mentioned a couple times in the past. This US$3.99 app runs on your iPhone, and you also must download a free app for your Mac. For those readers who use Windows, there's also an app from that platform.
Install the desktop app, then start the iOS app. The devices will pair over your WiFi network
