I'm posting this in case somebody runs into the same problem I had.
I noticed that my Pclos installation could not play multiple audio streams. For example, I use Clementine to play background music while I work, and if I clicked on a youtube video the sound wouldn't play.
I knew that it was not a hardware problem since it's a dual boot machine and in Windows I could always play several streams at a time.
Reading through other posts in the forum, I found some people with similar problems had to do with the general installation of the audio drivers. OSS drivers can't play multiple streams but ALSA drivers can.
I found out that I had already installed ALSA drivers, so in my case the solution was as simple as enabling Pulse Audio and rebooting afterwards... Voilà! Now I have background music and I can hear sound from other sources as well. I can even control the stream volumes independently in the volume mixer (Kmix).
I hope this helps somebody sometime.