Try to allow recording of an already playing stream.

You're probably using a kernel driver for your virtual sound card and when audio is going through it you pipe it too through the real sound card of the machine, but you're only selecting your virtual card as the default one when it's actually a recording stuff.

That prevents the recording of an stream that's already playing (since the program would be using a connection to the default sound card that at the time of playing was the real one). Maybe a filter driver instead would allow the recording but then the audio would go through the system mixer before you're able to record it.