I have 6 slots and 190 MEL power, but i was wondering if getting rid of 40 or more att and replacing them with s-grade augment would have an heavy impact on my DPS

it will depend of the augment but in the moment just wait we don't have the best S-grade augments

It depends but generally speaking, S-class augments > regular augments (at least when it comes to damage ones).

Yes, but you're good to wait for now, we don't have that good good yet

depends on the S-grade but tbh we are still missing alot of the better ones,at mo i'm only running 2 S-grades and 4 normal Affixes.