I have exactly the same problem as Rose, and I cannot see getting a different soundcard or 5.1 speakers is going to make the blindest bit of difference. Escpecaly no difference to Divx movies.
I suppose one solution may be to use a great program like virtualdub to rip the sound channel out, then use a great program like audacity to raise the total volume level of the resulting sound file. Then go back to virtualdub and rejoing the video and new audio.
This is a long-arsed and not tested method, is there a better one!!?
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Now we know how viral bunny signatures really spread.