TuneBlade

TuneBlade is a system tray application that lets you stream system-wide audio to AirPort Express, Apple TV, AirPlay-enabled speakers and HiFi receivers, and to AirPlay audio receiving applications such as ShairPort, XBMC/Kodi, and TuneAero.

It can stream to multiple receivers simultaneously. Its 3-band sound equalizer lets you tweak lows, mids, and highs easily.