I was thinking of undervolting and underclocking an i3 2100T (TDP of only 35W) for my next HD-HTPC build. But now I've just stumbled on one of these little boards: E35M1-M PRO
(18W) from Asus with Integrated AMD Zacate™ graphics. Both are capable of bitstreaming Dolby TrueHD and DTS-HD.
I need to to more research.
Thanks for all the replies guys.