So i think the decs are worried about making coherent sense but also worried about how stacking might imbalance the game.

Here is a possible solution.

Both items, say you have a cortosis shield and an armored drop suit.

Suit has defensive 1

Shield has defensive 2 and deflection 2

Now if we assume they dont stack, that doesn't preclude the second item still is beneficial.

What if you rolled the greater of the two items, in this case the shield and roll its 2 setbacks on your rolls.

However if the attack got through you could re roll a number equal to your second rating in this case if its melee or brawl attacks i could use my armors 1 defensive to roll a new setback die.

You could either swap out a setback for a setback from the original roll or eliminate all the former setback dice and only roll the secondary rating. In this case replacing the 2 dice with only 1 rolled seI could see trying either to see which way works better.

This sounds pretty fiddly to me honestly, I feel like it'd slow down a dice pool system which can already take some time to interpret.

There's already an inherent benefit to having two weapons with defensive; it's incredibly easy to be disarmed in this system, so you'll likely be losing that Defensive quality pretty often if you just have one.

Genesis and starship combat approach with just capping at 4 works imho like a charm.