I know have more time to fully answer this original post:
GreEn`mArine wrote: "...one thing that really bugs me right now is that there doesn't seem to be ANY balancing of the sound volume levels at all. When playing v2.4.2 I have the feeling of having some kind of 'constant' sound level/loudness. In current Nex SVN, this is absolutely not the case. ..."Just to mention examples: I can barely hear the switch-weapon-sound or the weapon-pickup-sound. There are a lot more other things that feel weird but would need more time to figure out what exactly it is. Apart from that, almost all of your sounds use very high frequency..."
On the subject of 'balancing sound-levels': My recordings are recorded professionally using 24-bit digital sampling and are not 8-bit sounds from regular open source like the original Nexuiz sounds were. (That's why they all sounded so similar and 'even'.)
My sounds have variable sound-levels dependant on the situation at hand. For instance, in real life, the sound of you picking up a gun should NOT be 'balanced' to be the same sound-level as a rocket-launching.

Why WOULD you want all the sounds in Nexuiz to be the same exact level? (Yes, I purposely turned those two files's sound-volumes down.)
However, when you refer to "too high a frequency", ...are referring to high-pitch 'treble', or the volume? Please keep in mind that exact terminology is very important when talking to an experienced sound-technician like myself, because certain words mean VERY different things.
With more than 20 years in this field, I HAVE to stick-up for myself and tell you that NONE of my sounds have a frequency that is "too high". (I record in 24-bit at 96000 Hz, but I publish my ".wav" sounds for Nexuiz at 44100 samples per second using 16-bit digital sound. Similarily, I publish my .ogg files as; 128Kbps, 44100 Hz with a ratio of 11:1). These are both CD quality releases, whereas the old Nexuiz-sounds were mainly recorded at just 22050 Hz, which is only HALF of my sound quality.
For your reference; I purposely level all the weapons to just 88% of maximum-frequency, so there is never any clipping or distortion, and most of all, so that players are not subjected to constant excessive noise. Because THAT is what burns your ears out and causes deafness. To do any different would be highly irresponsible of me, and I DO care about the players well-being.
You listed your headphone's frequency response, but you didn't list if your PC equalizer was set to flat. This is a MAJOR problem, because that's one-half of a possible solution which you chose not to answer.
Also, after doing comprehensive research on your headphone-model (Medusa), I found they are made of plastic and the internal parts are glued together with epoxy-glue (resin).
Something I politely want you to know; Epoxy-glue eventually loses it's flexibility due to body-heat, time, and usage, it therefore becomes brittle and most commonly breaks-off inside the headphone itself, causing 'rattling'. It may not be how long you've had the headphones, but rather - how long were they sitting on a shelf before you bought them, and what they may have been subjected to (heatwise, and possible collision-damage) even before you purchased them, ...hence, it may not be your fault if they aren't producing clean sound. This is an ever growing problem with most headphones today.
So, if one other person agrees with you here that they're also having 'distortion' problems - that merely means they have the same problem with their headphones, ...not that my sounds are at fault.
GreEn`mArine wrote:This is just my very own critical opinion, so you can also just ignore it

. I tried to be as honest as possible.
I will keep that in mind, because until you also have a sound-studio with the equipment available to accurately measure my sound-frequencies and THEN find fault with them, ...I will listen to the majority here - which seem very happy with my sound-quality.
(Particularly - the Developers opinions count most of all to me - because they influence the outcome of Nexuiz's evolution.)
I sincerely hope you have taken all of this in the way I mean it - with my upmost care and kindness towards you, ...and not as brash Counter-criticism of your opinion, which I DO respect completely. I always take positive advice to heart and do my best to accommodate as many as I can, ...unfortunately - I cannot always please everyone. I hope you understand.
Thank you for your honesty,
Cheers,
~Michael 'Tenshihan' Quinn