Neku,
Technically, there is a EXTREMELY slight possibility that ULib could be doing it.
We did have to write our own file handling code because Garry's was broken for some time.
However, considering that we've had many report success in using downloads.txt to send sound files after they asked for help here in knowing how, I'm 99.99% sure that it's not ULib.
Funkster,
First, the installer is several months, 2 months shy of a year in fact, old.
There have been many updates and bug fixes to our codebase for both ULib and ULX since we 'released' in August of 2013.
I'd strongly recommend obtaining newer code from our github repository using the zip file download link.
Second - your issue sounds like
a) Gmod is trying to bzip the files and breaking them. Not sure why/how it would break them.
and/(OR)
b) Your dedicated server host is trying to gzip the audio files and doing a horrible job of it.
Unfortunately, could be a combo of both.
Neither of which the Ulysses code could help you with.
Those are my educated guesses, and I could be incorrect.
Definitely update your ULib/ULX code to rule out it's not our file reading routines.