NeuroVoider

The first boss isn't so bad once you know what you're doing. For this one, pick Fortress and the Self-Repair skill. Now focus on fully upgrading only your orange items. Also have 2 Orange Rockets equipped and fully upgrade those. They deal such a high amount of damage, the boss will be dead before it knew what hit it. Disable the turrets, and focus your fire on the enemies real quick, then on the boss itself until it's dead.