What Hobbes said. Past that, unless I have overlooked or forgotten something, Shadowrun 6e has very simple and specific general rules on what does not stack: attribute augmentation past +4 and skill augmentation past +4. That's it.
There are some specific case rules regarding things that do not stack written in the description of specific items, such as bone density not stacking with other bone modification, or muscle toner being incompatible with any other agility augmentation, but all of those specific cases are noted.
By RAW, I don't even see any wording that says you can't stack the same instance of the same spell with itself, such as 4 casts of combat sense stacking.
Personally I don't think the same instance of the same spell should stack with itself (no armor twice, but increase attribute of two different stats yes), but that is simple not what the rules state, so unless I missed appropriate language tucked away to prevent that somewhere, until errata occurs (sigh. . .), it works by the rule set, though your GM can house rule otherwise. The same thing applies to cyberlimb armor - it stacks into infinity. Not even initiative has a general rule of not stacking anymore, although most of the articles that increase state a specific rule preventing it.
