Can't record the final mix in Rosegarden

Hello there. I'm relatively new to 64 studio, and so apologise if my question has an obvious answer that I've overlooked. I just installed version 3, and it all seemed to be working fine - I spent a happy few days putting together a fugue in Rosegarden. However, when I come to record the final mix of my fugue, Rosegarden just writes an empty WAV file. Rosegarden looks as though it's recording, but the file it writes contains only silence. As far as I can see, I've set the audio track up correctly - at least, it says the recording source is "master" (perhaps it's worth mentioning that the level meter, in the bottom-left of the screen in the audio track section, doesn't look like it's receiving any sound, when the composition is playing). Rosegarden also says that it's running fine under Jack, so I'm pretty confident the problem isn't there. I suspect that I need to do something with the ALSA mixer in the terminal - I've tried selecting various capture sources there, but none of them seem to do the trick. Perhaps this is related to a problem I'm experiencing with Audacity? Rosegarden and Audacity won't run alongside each other. If I've Rosegarden running, and I open Audacity (either manually or within Rosegarden, by editting an audio file), then Rosegarden immediately stops working. That is, when I click the 'play' button in Rosegarden, if Audacity's open, then it just won't play - not only no sound, but not even the counter turning. Once this has happened, Rosegarden won't start running again until everything's been closed down, the jack server restarted, and then everything opened back up again. My soundcard is a Soundblaster Platinum, by the way. I'm pretty sure that's not where the problem lies, though, since Audacity was working fine on my last Linux installation. Anyway, I hope someone can help! Thank you.