Make sure your using the latest drivers from creative. Then check the mixer program for your volume levels. Post here again if you dont get it fixed.
One reason might be if they are unamplified speakers the Audigy does not have an internal amp, so you will probably need a new set of speakers with amplifier built in.
If you are looking for new speakers, the 2.1 Klipsch are great for high end 2.1 setup and for low-end 2.1 I'd get a Yamaha set. 4.1 system I like the logitech Z560s.
Athlon XP 1700+,KT266A,Geforce3, Audigy.. 'nuff said.