The following is in the FAQ:
“Can I set the audio output on Syrinscape?
Yes. Syrinscape will stay attached to which ever audio driver is DEFAULT at the moment it starts. So Set the audio driver you want Syrinscape to talk to as DEFAULT, then start Syrinscape then you are free to change your DEFAULT audio driver and Syrinscape won’t notice. Using this trick, you can point Syrinscape at a virtual audio driver and pipe the audio down a chat client for online play. See more info for online play here: ProTips for Setting up Syrinscape”
The answer to that question is no, no there is not away to "set the audio output [in] Syrinscape; but farther down in the FAQ it also asks that we make suggestions so here is mine (in case you have not already guessed).
For the love of God and Country please add the ability to assign an audio playback.
The application is really nice, but the lack of this feature is just…well insane. Why do I have to manually change my default audios to what I want Syrinscape to use before I open the application, and then once the application is open I can change it back to the default I want; or I have to install a few pieces of software so I don’t have to go through the process of re-assigning my default sound devices?
I am sure I am not the first, nor do I suspect I will be the last (until this feature is added), to request this feature; so please add this into the Syrinscape. PLEASE!