A unit attacks another equipped with cursed signets in 2 ranks.The attacking die roll has surges and an accuracy. The attacker uses the surges to assign bane tokens. Are the wounds assigned in step 6 or later when the accuracy could be used to wound a figure upgrade in the front rank.

The wounds are suffered at the exact same time that the banes would be assigned normally.

As the ability doesn't modify the attack, just replace the bane effect, it would happen in Step 6.