QUOTE (Fastball @ Jul 23 2009, 05:50 PM)

Allow me to give you one more illustration.
The Combat Sense ability increases reaction for surprise tests. Suprise tests require an initiative test. Thus, by your interpretation, Combat Sense is a magical increase to initiative and cannot be combined with Improved Reflexes.
On SR4A page 104, however, you will find a sample character that has Improved Reflexes 2 and Combat Sense 2. The only way this is possible is if Combat Sense is not considered a magical ability that improves initiative. Since it is clearly a magical ability, it must be considered an increase to reaction, not to initiative.
Combat Sense isn't improving your initiative score.
Really, what needs to be determined is what quantifies an initiative booster/enhancer. To me the rules seem fairly clear cut on it. Initiative is Reaction + Intuition, and it says that any enhancement that affects reaction or intuition affects initiative. (Personally I don't see why these would be incompatible with improving Intuition, but meh)
What are all the methods to improve initiative? As far as a I can tell, the list is as follows.
Improved Reflexes (Adept Power) (Cannot combine with Magical/Technological Initiative increases)
Improved Physical Attribute (Adept Power) (No restrictions listed)
Reaction Enhancers (Cyberware) (Is compatible with other Initiative boosters)
Wired Reflexes (Cyberware) (Cannot be combined with any other form of Initiative enhancement)
Move-by-Wire (Cyberware) (I don't have Augmentation, I'm assuming it's identical to Wired Reflexes)
Synaptic Boosters (Bioware) (Cannot be combined with any other form of Initiative enhancement)
Suprathyroid Gland (Bioware) (No restrictions listed)
Cram (Drug, +1 Reaction) (No restrictions listed)
Jazz (Drug, +1 Reaction) (No restrictions listed)
Novacoke (Drug, +1 Reaction) (No restrictions listed)
Psyche (Drug, +1 Intuition) (No restrictions listed)
(Insert more drugs here that are listed in Arsenal)
(Insert any genetech/nanotech from Augmentation here)
Both the Suprathyroid Gland and Reaction Enhancers I could see having legitimate concerns on combining with the 4 IP improving enhancements. Reaction Enhancers because of it's exception in description, and Suprathyroid by whether it constitutes a technological improvement. Supra is slightly more complex in my opinion, so I'll address Reaction Enhancers first.
The overriding question here is whether or not the exception listed in Reaction Enhancers description overrides/negates the exception in the descriptions of the 4 IP improving enhancements. There's two ways to interpret this, the first is that due to the similarities between Reaction Enhancers and Wired Reflexes, the developers wanted to be able to use Suprathyroid + Reaction Enhancers, and were concerned about players mistaking it. The second interpretation, which I believe more likely, is that the Reaction Enhancers exception negates the exception in the description of the IP improving enhancements. As for the argument as to whether Imp. Physical Attribute being the Adepts version of Reaction Enhancers, I see nothing in the books to support that claim. If it were to be the adept's version, then I would have expected to see an exception in the description of Imp. Physical Attribute, which there is not.
As for why I see Suprathyroid being an issue. Improved Reflexes does not combine with magical and technological methods of improving initiative. This means that any natural method of improving initiative would combine. It boils down to what defines technological. I believe it is unanimously agreed that drug based initiative improvements do combine with Improved Reflexes, but not the other three methods of gaining IPs. However, technological just means that it came about due to improvements in technology. That means that since most drugs are synthesized/created, they are the fruits of technology, and thus technological. I suggest that if drugs stack with Improved Reflexes, then so must a Suprathyroid gland. Bioware is described as follows, "bioware augments the body's own functions and is integrated as if it were a natural feature." So to me, why bioware is obviously a much higher application of technological improvement, it is far closer to natural than drugs. So if drugs combine with Improved Reflexes, I believe that bioware (and genetech) should also combine with Improved Reflexes.
So basically, my interpretation is as follows.
Improved Reflexes (Adept Power) - Combines with Reaction Enhancers, Genetech, Bioware, Drugs
Synpatic Boosters (Bioware) - Combines with Reaction Enhancers
Move-by-Wire (Cyberware) - Combines with Reaction Enhancers
Wired Reflexes (Cyberware) - Combines with Reaction Enhancers
Also, Karma increases to Reaction/Intuition would combine. They adjust your base reaction/intuition, not enhance or improve it. Otherwise Wired Reflexes would entirely override your reaction stat and ignore your intuition score for determining initiative.