I'm 99% sure the 2010 mini used a 330m. Thanks for the AVS forum link as well. I've visited them before, but I got most of my info from the Plex forums (my HTPC front-end of choice).
Also, I think the previous gen minis couldn't even attempt streaming HD Audio formats, but again this is my first HTPC so I can't say with any degree of certainty.
Here's a link I found on apple support forums that seems to back this up. If that info is correct, the new mini might not support those formats even if the new hardware could potentially handle it.
I'm running a 5.1 setup myself in a small to mid-sized room and while I can hear the difference in True HD blu-rays, I'm working on converting everything into digital format and a 1080p DTS/Dolby 5.1 RIP is good enough for my ears given the tradeoff in file size from an uncompressed blu-ray rip.
Out of curiosity, are you planning on picking up a new mini for a HTPC or are you using a more powerful BYO option?