I request that the feature be added to VLC such that multiple DirectX audio device numbers could be defined, separated by commas, on the DirectX audio device selection screen, such that audio playback would be routed to each device during playback, concurrently.
This is completely technically feasible. As a proof of concept, one can load two instances of VLC and have material played back concurrently to two separate audio devices on the system, simply by configuring each instance to feed its own output to one of the two desired DirectX audio devices.
I am proposing to take this functionality one step further, such that multiple devices could easily be used to simultaneously listen to the same content.
This would allow things like enabling the use of a pair of USB headphones along with another pair of headphones plugged into the on-board sound card output, simplifying the implementation of group listening environments of multimedia content.