Native 5.1 or 7.1 support inside the Shadow streaming client.
Pull the exact number of channels and speaker setup either from windows/mac, or direct from the EDID information (if Ghost). Be able to override within Shadow in case the info is wrong.
All, but especially Ghost
Although some users have found a way to workaround and offer 5.1/7.1 sound on the windows client, innate support for multi-channel audio would be awesome, especially on the Ghost.