If you slide the Rolloff Factor all the way to the left, you will hear pretty much every sound in the entire sim.
Distance Factor:
Moving this slider to the right decreases the distance at which you hear sound effects (e.g., you'll no longer hear sounds that are further away).
Rolloff Factor:
Moving this slider to the right causes sounds to decrease in volume more rapidly as they move away from you. Moving it to the left causes sounds to remain louder as they move away from you.
Moving this slider to the right decreases the distance at which you hear sound effects (e.g., you'll no longer hear sounds that are further away).
Rolloff Factor:
Moving this slider to the right causes sounds to decrease in volume more rapidly as they move away from you. Moving it to the left causes sounds to remain louder as they move away from you.
http://secondlife.com/knowledgebase/article.php?id=335
Slide both of those all the way to the left and I suspect you will find you have plenty of sound.
Also, you can set your wind, footsteps, and UI volumes down low, which will make the wav files people upload louder in comparison - then adjust the sound effects slider to get the right balance between all the SL wind, footsteps, and UI sounds and the other sounds from your computer.
Audio and Video stream volumes are independent of the other SL sounds mentioned above.
Maybe that will help.