This is a simple doubt, I am trying to build a stupid moronic unarmed bard. Musical instruments go in the second hand and the attack animations are unarmed. Does the game actually counts attacks with an instrument equiped as unarmed? Or it does count the main hand as unarmed and the off hand as something else?

Thanks for the answer!

So the game treats a unarmed bard holding an instrument as a toon punching enemies and holding a shield, so since the unarmed attack is not a "dueal wield" per se it would not affect feats like Epic Weapon Focus (unarmed strike)?

Unarmed is unarmed no matter how you slice it. Feats are called "Unarmed Strike" just to confuse us I suppose. Same deal, though... attacking without a weapon. Creature weapons are also considered unarmed strike to some extent.

Fists cannot dual-wield (as odd as that may seem at first glance). The game doesn't consider two fists as two weapons. Neither does it consider fists as being wielded by the PC.

You can use the "spare" hand to hold anything you want that is not a weapon... shield, instrument, torch... whatever. It doesn't affect the unarmed strike in the least except monks will lose special abilities holding a shield. Bards will notice no difference.

All these feats benefit fighting unarmed:

Weapon focus: Unarmed strike (+1 AB)
Epic Weapon Focus; Unarmed strike (+2 AB)
Improved Critical: Unarmed strike (dbl crit range)
Improved Unarmed strike (avoid AoOs)
All the Stunning Fist feats (immobilizing attack if not crit immune)

Got it. Thank you.