I have the 5.1 channel version of this same head unit. It's a FANTASTIC machine. (Though technically it is 7.1, but you need a pre-amp for the rear two channels). The audio quality is down right superb, from gaming, to watching blu-rays, to listening to FLAC audio. I paired it up with a Sherwood speaker kit, couldn't be happier.
My only beefs: the HDMI ports don't take kindly to speakers falling on the things connected into them, ha. I did lose one port like that. Also, I'm not SURE on this one, but on mine, the main menu is not accesible via HDMI, and it doesn't do any upconverting, meaning if you have something connected to the component or composite video, then it will only output through the component or composite video hookups. Not that big of a deal, but I was using it for a while hooked up to my PC and to a 23" PC monitor which had only HDMI, so that was a pain!
Also, DONT LOSE THAT MIC! It works well, but if you lose it, it's something like $50 to replace. Totally ludacris if you ask me, it's really cheap and plastic. Though I suppose it's accurate, worked well for me. (Lost mine though. Heh, when your done with yours, wanna send it to me? :P)