Não, os Ataques desarmados não recebem o bônus de Ataque Poderoso de duas mãos.
Os Ataques Desarmados não são capazes de serem empunhados com duas mãos, nem são armas naturais capazes de serem empunhadas com duas mãos (ambas caem nas categorias Monge) e, portanto, não recebem o dobro do bônus de ataque de poder.
Atacando com um ataque desarmado de outra pessoaEu acho que - se você pudesse arrancar o braço de alguém, você poderia, por duas vezes, manejar um ataque desarmado, mas provavelmente seria apenas uma arma improvisada.
It's possible—and hilarious—for an attacker to employ a foe's unarmed strike by using the grapple action Use Opponent's Weapon (PH 156) (unless the DM says the foe's somehow not holding his unarmed strike). That makes grappling someone and saying Stop hitting yourself! a thing in D&D.
Decisão do DM
Com a autorização DM, no entanto, ao dar um soco duplo em Star Trek, você poderá receber um bônus de duas mãos.
Soluções de Talentos
A façanha Hammer Fist de Races of Faerun lhe dá um ataque especial:
You add one and a half times your Strength bonus on your damage when you hit with an unarmed strike. You must use both hands to make the unarmed attack.
O talento Hammer Fist from Dragon Compendium não exige ser um anão, mas afirma especificamente que você só pode fazer um ataque:
You may make a single unarmed attack with both hands to add 1-1/2 your Strength bonus on the damage roll.
Referências
A monk’s attacks may be with either fist interchangeably or even from elbows, knees, and feet. This means that a monk may even make unarmed strikes with her hands full. There is no such thing as an off-hand attack for a monk striking unarmed. A monk may thus apply her full Strength bonus on damage rolls for all her unarmed strikes.
Natural weapons are weapons that are physically a part of a creature.
On your action, before making attack rolls for a round, you may choose to subtract a number from all melee attack rolls and add the same number to all melee damage rolls. This number may not exceed your base attack bonus. The penalty on attacks and bonus on damage apply until your next turn.
If you attack with a two-handed weapon, or with a one-handed weapon wielded in two hands, instead add twice the number subtracted from your attack rolls. You can’t add the bonus from Power Attack to the damage dealt with a light weapon (except with unarmed strikes or natural weapon attacks), even though the penalty on attack rolls still applies. (Normally, you treat a double weapon as a one-handed weapon and a light weapon. If you choose to use a double weapon like a two-handed weapon, attacking with only one end of it in a round, you treat it as a two-handed weapon.)