question on brown equipment sets

[Mr.Pibbs]

for master refiner and master extractor equipment sets do u need all pieces to have increase chance of more psi materials or can u just have 2 out of 3 pieces for that, and does this only affect psi materials extracted from those stones?

[Hemmingfish]

You need all three pieces for the bonus. That's what the number in brackets means.
From what I can tell looking at the code, the set bonus doesn't actually affect psi stone extraction at all. Instead, it boosts the psi stones that you get as enemy drops. Some of the individual items boost extraction though.