What is not clear to me though is that this is a ChucK issue.
Yeah, I'm pretty sure it's not a chuck issue per se.
You could also do it internally, by chucking the dac to WvOut and so having ChucK record all that ChucK does. That last option might be the most simple one. There is a example file that demonstrates this, have a look whether it suits your needs.
Recording the audio is not a problem, I know how to do it using ChucK. I really just wanted to get a video of my desktop with chuck running. An option would be recording audio and video separately and mixing them afterwards but that is not so nice and I'd like to avoid it. Anyway I know this is kind of a complex question... I'll try jack again later and report the results (if I come back alive :)