I usually treat this as a two-part problem, using the wired reflexes / reaction enhancers guideline.
Wired reflexes are a two-part system: the Reaction boost, and the Reflex (initiative) boost. Reaction enhancers increase only Reaction. They don't stack with reaction enhancers, except for when you have both of them on wireless mode; choose one or the other. However, when the person who has both isn't running them both on wireless, he can choose which one applies to each increase; he could have, for example, the reaction enhancers applying to Reaction, and the wired reflexes applying to Initiative.
In my mind, the same goes with any other multiple-enhancement system; the FAQ supports this interpretation. If you have multiple boosts to X, you have to pick which boost applies from time to time. Since the suprathyroid gland supplies only a +1 Reaction, and Improved Reflexes supplies its level, at any level besides 1 it makes more sense to apply the adept power.
Overall, however, it's stated that things don't stack - but remember also that reaction is now seperate from initiative.