I guess this is better suited for the AoR board, but I know this board gets more traffic.
Dynamic Fire is a talent that is only found in the Recruit tree, the universal specialization from AoR. It reads:
When making a ranged attack while engaged with an opponent, the character may suffer 2 strain to reduce the ranged modifier added for being engaged by 1 for the attack. So, when firing a Ranged (Heavy) weapon, the character only increases the difficulty by 1 when engaged, and when firing a Ranged (Light) weapon, he doesn't increase the difficulty at all.
And the Forearm Grip attachment is found in both the EotE and the AoR CRB. It reads:
Decreases the additional difficulty of making Ranged (Heavy) checks with this weapon while engaged to an additional [1 Purple] (rather than [2 Purples]).
So both say they decrease the difficulty, but then both specify that it goes from 2 to 1 (on Ranged (Heavy)). Just reading the wording, my gut tells me that the attachment is always from 2 to 1, however the talent could further modify it as I see the spelling out of going from 2 dice to 1 as more of an example of how it would work rather than the hard rule.
However, I could see them not able to overlap at all. Just curious if anyone has seen this brought up or maybe I am missing something. I plan to mail the devs about it as well.