Since nobodies jumping in, I'll give my 2 cents.

Does STS system elementate the need for string silencers?

I would say that it would eliminate at least one. I plan on running a solitary string leech or cat whisker on top.

Is there a thoud or popping sound when the string strikes it?

I hear a slight thud myself.

And Does it effect the tune of your bow and is there a speed loss or gain when using it.

No speed gained or loss. The only way I could see it affecting the tune is if your set up was previously dialed in to account for any nock point travel that occured past the idle brace height of the bow.

idle brace height of the bow I'm sure there is a fancy archery term for what I'm trying to say, maybe this will help- (foreward movement of the string during the shot sequence which occurs beyond the measured brace height towards the riser)