cartridge headshell screws.

"I am pretty sure the alignment and azimuth were the same". Highly unlikely! When you replaced the screws you inevitably ended up changing the cartridge alignment and other performance parameters and THAT is likely responsible for 90% of the change you are hearing. Can screw materials, torque and some of the other variables mentioned impact the sound? Probably, but only slightly and it is doubtful you would hear it. The change in sound quality you describe is far too great to be accounted for by these variables. However, even the slightest change in alignment, azimuth, VTF will alter the sound in the way you describe.

Dear t. : During the first 50-60 hours of playback in a new cartridge almost every day the sound is changing. Sometimes only a little and sometimes in greater way and this broken time can be affecting what you are listening.

Maybe you have to wait for at least those playback 50 hours till de cartridge is already settle down and then do te screws tests again.

regards and enjoy the music,
R.

Right.  I know.  The difference to me was noticible enough to post it.  IThrough many trials and tribulations with this table I have a good feeling for the sound it produces.  I guess I am just surprised at the difference a screw can make, whether it is the weight, material, etc.  Pretty amazing. 

@tzh21y. I totally understand. After spending over a year (on and off) with a cartridge that turned out to be defective, I tried everything. Brass, Ti, SS, a heavier counter weight.... it was exhaustive. I kept some Titanium headshell screws (accidently bought 2.5 instead of 2.6s) for their light weight and started over with a new cart. Although it didnt have the distortion of the defective cart, it was super rolled-off in the mid treble region (I'd guess 10k -14k range). So cymbals and acoustic strings sounded muffled or way down in the mix. I've messed around with that cart trying more VTA, less and then more VTF, zenith, etc. But I never expected what I tried next. I removed the Ti screws in favor of SS screws. And wow, I finally have 'cut' to my music again. Huge difference indeed. I ordered brass just to see what they will sound like. I suppose as the other user said, part of it could be torque but with little distortion and just lacking treble, I'm doubtful. Either way, I recommend experimentation with headshell bolts. You might be surprised, as tzh21y and I are. And for the record (pun intended) I had no idea what to expect with the results. So my Google search brought me here.