Quiet Weapons? (SB Audigy Users) I found one possible solution for you
If you're having problems with quiet weapons while the world around you seems to be screaming with all its might, you may want to try this. It worked for me, so that's why I refer to it as a "possible solution."
Go into the "Creative Sound Mixer", then click "Settings", and then make sure that your "Bass Redirection" is checked. Also make sure that you have EAX turned off by going to "EAX" and then "Advanced EQ" and then "No Effects."
And finally, make sure that your "Audio" settings in UT2004 is set to "HW+3D Audio".
This has helped my weapon volume by a decent amount. It's still not what I would expect when wielding a rocket launcher, but it's better than what I had. As always, YMMV.
Have a great day,