Depending on what you are planning to do, you might also want to take a look at
JACK - Jack Audio Connection Kit - which can be used to route audio to/from various inputs and outputs on your PC.
It's available in the repos of all major GNU/Linux distros.
And the routing can be as simple or as complex as you'd like it to be. You aren't limited to routing audio between physical ports, you can even route audio between any pieces of JACK compatible software you have installed.
Many Linux audio applications support JACK in one way or another. Sometimes JACK compatibility is built in, other times it is available via plugins.
Personally, I've only used JACK on my old laptop - to route audio from an external USB Sound-card and an external USB MIDI controller to DAW software like Ardour and LMMS - to create a home recording studio. But that laptop died a couple of years ago. I haven't got it set up on my current laptop!
Here's an example of a fairly complex bit of routing, for someones home recording studio setup (not mine, I found this on the web!):
You can see that the outputs of certain programs and bits of hardware are routed to the inputs of others.
The US428Control appears to be their USB audio interface, which I think is an old TASCAM interface. I'd guess that would be their main source of audio input. The other main source would be their virtual MIDI keyboard, which you can see gets its signals routed through a couple of programs, which in turn are routed elsewhere....
But even if you aren't planning on setting up anything as complex as a recording studio - JACK may come in handy. Again, it depends on what you plan to do with your audio!
Just thought I'd put that out there!
