Whenever I see this 'multiple apps using a sound card at once' issue mentioned, I try to recall what sort of ALSA 'voodoo' I've employed to make this work for me. Then I realise; absolutely nothing.

I think the last time I ever had this problem was literally around 12 years ago, and it was caused by me fiddling with my alsa conf file. I haven't touched any ALSA related settings or done anything special in the last ~8 years, and I never have a problem with things like playing music and having a browser flash plugin using audio at the same time.

Not saying it doesn't happen to other people. Just genuinely curious and baffled.