Most if not all Pioneer receivers of recent vintage decode WMA Pro. It isn't easy though. Your computer sound card drivers must support it and then you have to go into the options in Windows Media Player and check the box if it is available to enable it. If that works, your Pioneer will recognise the signal and actually sound much better than DD or DTS.
It is sent via S/PDIF or optical same as DD or DTS.
The format is not well supported by Microsoft however. The XBox 360 has an option that allows WMA Pro as an output selection. I have never been able to make it function on three different 360's. (The function does work for HD-DVD playback and sounds noticeably better.)