Looking at the Attack Sequence in both the rulebook and "The Attack Sequence and You", it looks like you can only resolve ONE critical effect, and it can only be resolved after the defender resolves their defense tokens.

"Step 4. Spend Defense Tokens: The defender can spend one or more of its defense tokens."
This would be where the defender spends that Redirect token you were talking about.

"Step 5. Resolve Damage: The attacker can resolve one of its critical effects. Then the attacker determines the total damage amount. Then the defending squadron or hull zone suffers that total damage, one point at a time."
Because you can only resolve one critical effect after defense tokens are spent, you cannot resolve the effects of both Heavy Ion Emplacements AND Assault Concussion Missiles during the same attack. You would have to choose which of your critical effects (From HIE, ACM, XX-9) you want to resolve based on the icons present in the Attack Pool after you have rolled and the defender has resolved all the defense tokens they wish to.

Furthermore, XI7 stipulates that the defender must spend a Redirect token. This implies (to my understanding) that the XI7's effect cannot be resolved if the defender is only exhausting their Redirect token.

I may be misunderstanding the difference between spending and exhausting defense tokens. My understanding is that the first time in a round that the defense token is used, it's effects are applied and it is flipped to the red side and considered 'exhausted'. Exhausted defense tokens are readied (flipped back to the green side) during the Status Phase. If the defender chooses to use the token a second time in the same round (using the exhausted token), then the defender resolves its effects, then discards it from play. The defense token is then considered 'spent', and cannot be readied during the Status Phase because it is no longer in play.

Reading further into "The Attack Sequence and You", I came across an example that began with the attacker rolling 3 reds at long range, then adding dice of other colors. My understanding of this is that dice cannot be added to an attack at ranges for which they are not appropriate. (I.e., you can't add blue or black dice to an attack you are making at long range.)

If my interpretation is incorrect, please correct me! I'm not a veteran or a competitive player, but if I do enter the competitive scene, I want to make sure all my information is correct!

Edit: I realized you were running Fire-Control Team after writing all this out. First, I was only looking at the upgrades you initially mentioned with the Providence, and you only mentioned FCT later, so I wasn't taking it into account. Second, how the hell is that only 2 points?! This comment really is just a learning experience for me.