The last official release of XBMC was version 11 known as Eden, a user (Daniela) managed to modify the audio subsystem of XBMC used in Eden to allow bitstreaming of TrueHD and DTS-HD, it is these builds contained in your second link, the thread titled
[WINDOWS][PATCH]Bitstream output of HD audio formats, these are generally known as the Daniela HD Audio builds. As these builds are built on a stable version of XBMC it is probably still the most stable version containing HD audio and will also have best compatibility with add-ons & skins.
For the last couple of years a replacement audio subsystem called AudioEngine (AE) has been under development by the XBMC developers, one of the features of this new audio subsystem is the bitstreaming of TrueHD and DTS-HD but it contains many other audio improvements as well. AE replaced the old audio subsystem after Eden was released in the May development cycle for the next stable release of version 12 known as Frodo, and since then development has continued to ensure all bugs are squashed and that there is no regressions in functionality compared to the old audio subsystem as used in Eden. The builds containing AE can be found in the Nightly builds contained in your first link, however you should be aware that as these as bleeding edge they can be unstable, for the most stable Frodo developement builds use the monthly apha snapshots at
Snapshots, you should also be aware that either Nightly or Snapshot development builds may not be compatible with the full range of add-ons & skins.
So to summerise, for best range of stability and compatibility with add-ons & skins the Daniela HD Audio builds are best, but as these were user produced there is no official support if you do run into problems. For official support and to use the audio subsystem that will in Frodo use either the Nightly or Snapshot builds, but be aware that these won't always be stable and won't be compatible with all add-ons and skins, however this will improve as Frodo nears release and they get updated for Frodo compatibility.
