The AVR X2000 supports Airplay. If you set this up on the receiver in your network you will be able to stream music from your iMac to the Denon by simply choosing the receiver as your output on the iMac. In iTunes you can even choose both the internal speakers and the receiver at the same time.
This from the manual:
1 Install iTunes 10, or later, on a Mac or Windows PC that is connected to the same network as this unit.
2 Turn this unit ON.
Set “IP Control” (vpage 161) to “Always On” for this unit.
NOTE
• When “IP Control” is set to “Always On”, the unit consumes more standby power.
3 Launch iTunes and click the AirPlay icon ' displayed the window and select this unit from the list.
4 Choose a song and click play in iTunes. The music will stream to this unit.