This is taken from avsforum -
Bitstreaming (or pasthrough) means that the HTPC outputs the untouched audio stream to the Audi-Video receiver for decoding, and all of the decoding process is done on the AVR, nothing is being altered on the HTPC. DTS/DTS-HD Master Audio/Dolby Digital/Dolby Digital should appear on the display of the Audio-Video Receiver. Botstreming can be done via the 2 available digital connections :
• Bitstreaming via HDMI - DTS-HD Master Audio*, Dolby TrueHD*, LPCM, DTS, Dolby Digital (AC3).
• Bitstreaming via S/PDIF - DTS, Dolby Digital (AC3), 2 channel LPCM.
*Note : Only the following platforms can bitstream DTS-HD MA & TrueHD :• ATI/AMD HD5xxx/6xxx series graphic cards
• Nvidia GT430 & GT520 graphic cards
• Intel Core i3 with integrated Intel HD 1000/2000 GPU
• Asus Xonar Hdav 1.3
Another option would be this -
http://www.newegg.com/Product/Product.aspx?Item=N82E16856119050