Wow, I am honestly baffled. With the PrC Contest, G7 and all, where do you find the inspiration to come up with something as awesome as this?
I love the flavour of the class, but I think Zenith's Revelry might be a bit too strong. Extra standard actions can completely break an encounter. I'd increase the bardic music uses required to use this ability and make it so that it grants extra move actions instead. That way, it should help out the lower-tier classes (mostly martial classes) more as it helps them position themselves better for full attacks.
There's a typo in Midnight's Requiem. You referred to it as Midnight's Dirge in the ability's description.
I'm a bit confused by Twilight of Death. Does this mean the Restless Troubadour gain all of the following effects while suffering none of their drawbacks, such as:
-An outsider's weapon proficiencies, darkvision and the fact that the no longer need to eat or sleep (although an undead also no longer needs to eat, sleep or breathe)
-All immunities given to Undead, yet selective so they can still benefit from mind-effecting buffs such as a Bard's Inspire Courage.
This might be way too powerful. I'd like it if you could pin down a few specific effects you'd be willing to give the character, as well as the ability to suppress them at will. It increases clarity and prevents unnecessary rules debates.
Other than that, love the class