"Any improvements to Reaction do thus increase Initiative
- Pretty sure the "thus" refers to the fact that an improvement to Reaction also increases Initiative.
, but the bonus from a Suprathyroid Gland does not directly affect Initiative Dice, like Wired Reflexes or Synaptic Boosters.
- This means that an item that boosts "Initiative" refers to the Initiative Dice
Thus, I would argue that the bonus is stacking so long as it doesn't give more than +4 bonus. The only circumstance in which someone can break that +4 bonus is with drugs."
- So the bonuses from Suprathyroid Gland and Improved Reflexes stack, so long as the character doesn't go above the +4 maximum for Reaction