[Apothis]

This box is great in some regards, - mega fast in the XBMC menus, but it has no 24Hz video output, and no AAC to PCM on the fly transcoding. The Raspberry pi can do the last two, which are pretty much essential for someone with AV amp and a big display.
Menus are very slow on the Pi though in comparison. Wish the Fire TV did 24Hz and ACC transcoding.

It will certainly transcode AAC to AC3 if you want. It cant transcode a 5.1 AAC to 5.1 LPCM due to the usual android limitation of only 2 channels of LPCM. But I just tested on a 5.1 AAC (had to hunt to find one) and it happily transcoded it to 5.1 AC3