This is a house rule I've incorporated but I'll throw it up for your viewing (dis)pleasure.
When using martial arts UNARMED, a success on Brawl AND martial arts skills allows double damage as normal.
When using a Weapon and Martial Arts the weapon still does normal damage, regardless. However:
A sucessful attack roll can be modified by the martial arts skill roll, if the martial arts roll is a critical, by 1 degree.
If the weapon or unarmed roll is a success and Martial arts roll is a critical , the weapon becomes a special success.
If the weapon or unarmed roll is a special success and the Martial arts skill is a critical, then the weapon roll becomes a critical.
I personally think doubling a weapons damage from a normal success is OP. This method seems to make my group happy.
It increases the characters skill and possible damage by increased chances for special and critical success, without making martial arts godlike.