I have the exact same setup as you. Firstly how are you connected, I have a thunderbolt to HDMI cable converter to make the connection, are you going HDMI to HDMI?, does your HDMI cable support audio ?, second you will have no volume control via the keyboard using HDMI for sound which is a real pain. I use Soundflower to get over this and have a very happy audio setup (google how to set it up)
Soundflower over rides this.. I have full control of audio via keyboard and remote. google soundflower and mini mac.