This is just a quick response. I will test the files and post the impressions afterwards. Thanks a lot, Tripredacus !
1st link: I read the article. Well written. Does not apply to my power supply. It's 3 months old, it's a good power supply, I read trusted reviews about it (with oscilloscope diagrams of ripple and noise, all sort of measuring depending of load, temperature and so on), it produces good voltages and (well inside limits) clean direct current. If you are talking about the sound card, yes, I am aware everything has it's lifespan.
2nd link: [yawn]
3rd link: Correct. Basically, same as 2nd link. You could have also posted a link with human capabilities over time. Same thing. Times forgives no one.
By "we" do you mean you and jaclaz ? Because I'm not clear. Where do I stand, between a totally def and audio moron and an audio god ? I think I have a pretty good idea of how sound should be, relatively to my equipment. I am aware this is not thousand of dollars equipment, but taken into consideration this, I'll say something is definitely wrong, but don't know where.
Also, from experience, you may encounter some discomfort at the higher frequencies... also it may be possible that dogs in your area may not appreciate when the high frequency range ceases to be heard by you.
Of course (and to partially answer my own question above), I'm not a totally id***. I have ears and can detect the raise of volume and/or potential dangerous levels. For this, my finger is always on the stop button. I already played with some of tone generators from links given by jaclaz and have a pretty good idea of what I'm doing.
Never mind the dogs, they must be def, they are barking all night under my window and not letting me sleep. If I'd be certain my speakers could do it, I would actually pay them back.
I thought audio part is not OS dependent. What (and please try to think if you can find an answer) I don't get it is why games and movies sound ok, crisp and loud and only music sounds crappy. My only assumption is that music is more rich in harmonics and this puts a lot on the capabilities of the sound card. I mean, on simple music, it sounds ok, but as soon as heavy and complex instruments kick in, sound gets distorted. "s"-es don't sound clear, it sounds like 'sh"-es (hope you understand), I hear harmonic distortions and clipping occur.
OK, wire management is crap inside my computer, heck, I always get horrible distortions in sound when one of my four HDDs is working at high transfer speeds. You might be on to something here. I'll try to shield somehow the cable from sound card to front panel. Thanks Creative for not thinking of that.