Hey Oggy...
"So if the second weapon has penalties or bonuses that would affect the pool, such as adding Boost or Setback dice, these would not apply. However, if the second weapon has penalties or bonuses that are applied after the pool has been rolled, then those penalties or bonuses do apply if you trigger the second weapon to hit."
Would that mean that if the 2nd wpn has BAM and is triggered due to the 2 Adv rolled by the first weapon...That you DO have to roll the 1 Setback Die???