It seems you haven't looked everywhere for your HTPC motherboard. Gigabyte makes one that does everything you're looking for, with the exception of it only supporting HDMI 1.2. Here is a link to it, http://www.gigabyte.com.tw/Products/...ProductID=2579
and if the link doesn't work, the model number is: GA-MA69GM-S2H
I know it doesn't say that it will playback Dolby TrueHD, or DTS HD Master audio, but, since those are technically lossy codecs, and this motherboard states that it will pass completely uncompressed audio, it should be able to handle "passing through" of any other codec. Then it would be up to your pre-amp or reciever to do the decoding.
Just my two cents.