JRiver cannot natively stream to an AirPlay-enabled device, Airport Express or Apple TV and will require the third party software
Airfoil from Rogue Amoeba to do so. Using Airfoil will also require that you do not bypass the Windows Mixer with WASAPI or ASIO.
Most file formats (WAV, AIFF, ALAC, FLAC, AAC, MP3) will stream to the Apple TV, but anything greater than 16/48 will be downsampled. According to Apple TV users on various forums, the
new apple TV will upsample everything to 16/48 while the Airport Express will stream files bit perfect (up to the 16/48 limitation).
Steve