Improve RDP audio latency

[James Teh]

Currently, the latency of audio playback when connecting to a VirtualBox RDP server is over half a second. This applies even when connecting to a VirtualBox RDP server running on the local machine (i.e. localhost). While this is probably satisfactory for many users, this is extremely poor for vision impaired screen reader users who administer remote VirtualBox machines. I understand that audio playback latency will never be instantaneous, but I am hopeful that this can at least be improved somewhat. Note that audio latency when connected to a Microsoft Windows machine over RDP is somewhat less than with the VirtualBox RDP server.