rework sound card management

[patty2901]

Virtualbox is a powerful software, but its audio implementation seems to be on a level from 1997. While technology has not changed fundamentally since then, there have been several changes in system setup of host and guest which cannot be handled by virtualbox. I think, the following features are urgently required:

(1) support for multiple audio devices
(2) selection for device mapping (guest<->host)
- at least an option "default device" (of the host system) should be available - in addition to a certain hardware item
- a configuration per guest device for multiple host devices including priority settings would be even better (which would enable a kind of "default device" implementation where device priorities differ from the host system's configuration)
(3) guest support for hot-plugging of audio devices (e.g. headset or usb devices which are _not_ guest exclusive)
(4) even better than (2) would be a big audio mixer which can route, level and mix any input (=guest output channel or hardware:microphone/line-in signal) to any output (=hardware:device output or guest record channel)
(5) guest support for low latency drivers (e.g. ASIO) which requires an additional low latency usage implementation for the host (if available there), instead of DirectSound

[michaln]

Contributions are welcome.