If you need to play sounds or TTS out of specific channels, you can do this from within the, 'Play a sound' action or the, 'Say Something with TTS' option.
If you need to change the default playback device for all of Windows (not recommended, but there if you need it - really left over as a legacy feature), that option is near the bottom of the Audio tab on the Options screen or it can be set from the command line (the command line feature is what I use a lot). This is what I believe you're using - don't use this.
If you need to change the default playback device for VoiceAttack's sounds or TTS, you can do this by changing the options, 'Override Default Playback Device' and/or 'Override Default Text-to-Speech Device' on the, 'Audio' tab on the Options screen as Pfeil was explaining. This is what you need.
Outside of that, there's no other audio functionality provided with VoiceAttack, unfortunately. Hope that helps!