Could be that you saved in DSS the data in stretched Format or only 16-Bit TiF. or ... ?
You should save the data in 32-Bit FITS in DSS so they should look similar to PI
but never the same!
Let us have your 32-bit FITS outcome from DSS and
the 32-Bit outcome from PI.
There are so many possibilities for the real or unreal differences
so with words ist not solvable.
Gerald