Although it's definitely possible to brute force your way into the higher lvls- (done it b4 but takes a lot of time) I recommend retrofitting & equipping at least one Disruption Charge weapon. If it doesn't show up in the retrofit menu, either u haven't unlocked it by now, or more likely you haven't enabled it because you haven't reinforced in a while. Also upgrade you weapon class to 4.0 if possible & equip & shard link as many of your resource/salvage shards & crew to lvl up your ships weapons & shields faster. Don't forget to temporarily turn OFF Your Void Becon or Void Lure in the synth modules screen as it will spawn 2-4x more enemies than normal while your trying to take out the boss.