I mentioned  5.7 as an example but really  i meant if u change the overall power levels. For example if u went from 762 down to 556 would it further mask your location. 
Due to there being less shockwave? Likewise, i know 5.7 is supersonic but surely it has less shockwave and thus it masks you better.

Are you referring to the supersonic shockwave from the bullet passing or the muzzle blast?

Both. I mean tge overall sound signature.  

Anyway on a random note, would suppresaors work with sabot or flechette rounds? Or would it affect sabot separation and accuracy.

I know the AAI rifle had a semi suppressor because it was so loud

That depends heavily on both the sabot and suppressor design.

That said, yes you can absolutely make a suppressor that supports sabots quite well. You do that by making a pepperpot style liner for your suppressor.

As for the sound of the "crack" from the supersonic bullet passing by, Emeric has written a paper on it, but I can't seem to find it at the moment.  Hopefully someone else will post a link.