Hi all,
I have the new Mini 2011, i7 6630 256 mb, etc. It replaced my early 2009 mini with the 9400m graphics.
In both cases, this worked for me;
I use VLC for playback in case of .mkv files and QT 7 for anything made with Quicktime like FCP X. (QT 7 allows you to replace the original soundtrack from your movie, pcm (uncompressed) to ac3 (compressed) which is Dolby Digital on your amp.
A Toslink cable from the headphonejack goes into my amp. I use the standard HDMI to DVI connector which is supplied with the mini that goes into my TV.
1. Delete everything that your mini doesn't originally have like Plex and such. You DON'T need it !
2. Go to this site and follow ALL instructions. (You'll only need to do this once)
http://fplanque.com/dev/mac/ac3-ac-3-5-1-surrond-sound-apple-mac-osx
3. Additional to these instructions; don't use the HDMI-output in Audio Midi Setup but the INTERNAL OUTPUT. When u select the HDMI-output in the left colmn, you'll introduce internal conflicts
Keep into account that the Audio Midi Setup has a tendency to jump back from 48 Hz to 44.1 Hz which results in the 'cracking noise' after a reboot.
The core-problem is that OSX doesn't pass the audio correctly through to your amp. Keep that in mind. Once you fix this, you can play anything you can throw at your Mini.
Good luck !
If you have questions, post them here.