Hi Yasuno,
that's an interesting use for a sound card

Wouldn't this work with IR signals as well?
At the moment I'm not aware of any possibility to play a specific audio file on a specific output device with EventGhost without a 3rd party tool.
Unfortunately it's not easy to program this (it is possible though), Pako did something similar as he created the intelliSpeech plugin.
What you can do: On most media player you can set a specific output, you can then use EventGhost to open audio files with that media player
You should make a post for that idea (using a soundcard as Transceiver) in the Feature Request Forum.
Me or someone else may pick it up some day and create a plugin for that.