Massive Spoilers!
So I finally got into the MPQ, and like a kid in a candy factory I jumped right in. :^)
Anub'arak's new dialog isn't particularly interesting, nothing lore heavy at all, just battle cries and such for abilities during the encounter. The Black Knight isn't anybody of interest as you were all speculating, just a random minion of Arthas. Jaina's voice actor has been replaced(or maybe just re-enacted), all her voice work has been redone as well from caverns of time and her greetings/aggro in Theramore.
This is my interpretation of the sound files, if anything is off, again it's just my own interpretation, don't want a repeat of "Sylvanas was at Wrathgate and they took her out omg!"
Tirion Alliance Arrival Dialog:
Varian: Tirion.
Tirion: King Varian, Lady Jaina, welcome to the tournament, your place in the Coliseum is waiting.
Jaina: Thank you, it's the least I can do to support this, we need to stand together.
Varian: You ask much of me Tirion, to sit and watch...trusting the savages to keep themselves in check.
Jaina: I'm sure Thrall will have his people under control
Tirion: My people are here to make sure that they honor the rules of engagement, it will do your subjects well to see you in the stands.
Varian: Perhaps, I doubt the effectiveness of this gambit, it would be better served preparing our armies for the final assault, but if my presence is required in these games to gain your support in the battle...then I will remain...for now.
Tirion Horde Arrival Dialog:
Thrall: Garrosh, I expect you to
control yourself here. I do
not want a repeat of the Violet Citadel.
Garrosh: Pah!
That was a show of strength worthy of a leader, I only regret I did not kill that human before the
mage interfered.
Thrall: We are guests here Garrosh, and you will conduct yourself
honorably.
Garrosh: What honor is there in thrashing about with bludgeoned sticks, this is a waste of time.
Tirion: Welcome Warchief Thrall, Overlord Hellscream.
Thrall: Thank you for the invitation Lord Fordring, we look forward to observing these games.
Garrosh: Speak for yourself
Thrall.
Tirion: I hope you will see the merit of these events in time Garrosh, we cannot win against the Scourge if we continue to war against one another.
Thrall: Wise Words
Garrosh: Words of a fool you mean! The Horde will destroy the undead without your aid
human, or that of a pompous king!
Thrall: Garrosh! Enough!
Garrosh: Pah!
Tirion: Under my roof
gentlemen, I trust you will behave.
Thrall: Of course Tirion, I apologize for his outburst, it will
not be repeated.
Tirion: If you will follow me then.
Argent Tournament Intro/Generic Monsters Fight(s):
Tirion: Welcome champions, you have heard the call of the Argent Crusade, and you have boldly answered. It is here, in the Crusader's Coliseum, that you will face your greatest challenges. Those of you, who survive the rigors of the coliseum will join the Argent Crusade on it's march to Icecrown Citadel.
Tirion: Steel yourselves heroes for the twin terrors, Acidmaw and Dreadscale!
Varian: Your beasts will be no match for my champions Tirion.
Tirion: Hailing from the deepest/darkest caverns of the Storm Peaks, Goremoc the Impaler! Battle on Heroes!
Garrosh: I've seen more worthy challenges in the Ring of Blood, you waste our time
Paladin.
*They die*
Tirion: The air itself freezes with the introduction of our next combatant! Icehowl! Kill or be killed Champions!
Tirion(You lose): Tragic, they fought valiantly, but the beasts of Northrend triumpthed, let us observe a moment of silence for our fallen heroes.
Tirion(You win): The monstrous minsarory(SP?) have been vanquished!
Jaraxxus Event:
Tirion: Grand Warlock Wilfred Fizzlebang will summon forth your next challenge, stand by for his entry!
Wilfred: Thank you Highlord! Now challengers! I will begin the ritual of summoning! When I am done, a fearsome Doomguard will appear!
Wilfred: Prepare for oblivion!
Wilfred: Ah ha! Behold the absolute power of Wilfred Fizzlebang! You are bound to ME demon!
Jaraxxus kills Wilfred: Trifling Gnome, your arrogance will be your undoing!
Wilfred: But I'm in charge her- *Anguished and wonderful Gnome Death cry*
Jaraxxus Aggro: You face Jaraxxus, Eredar lord of the Burning Legion!
Tirion: Quickly Heroes! Destroy the Demon Lord before it can open a portal to it's twisted demonic realm!
Jaraxxus Death: Another will take my place...your world...is doomed!
Garrosh: Treacherous Alliance DOGS! You summon a Demon Lord against Warriors of the HORDE?! Your deaths will be
swift!
Varian: The Alliance doesn't need the help of a Demon Lord to deal with Horde
filth! Come PIG!
Tirion: Everyone calm down, compose yourselves, there is no conspiracy at play here, the warlock acted on his own volition, outside of influences from the Alliance, the tournament must go on!
Tirion: The loss of Wilfred Fizzlebang....while
unfortunate...should be be a lesson to those of you who dare to dable in dark magic! Alas, you are victorious, and now must face the next challenge.
Alliance PvP Battle:
Tirion: The next battle will be against the Argent Crusade's most powerful knights! Only by defeating them will you be deemed worthy!
Varian: Our honor has been besmirched, they make wild claims and false accusations against us! I
demand justice! Allow my champions to fight in place of your knights Tirion! We
challenge the Horde
Tirion: Very well! I will allow it! Fight with honor!
Garrosh: Show them no mercy Horde champions! Lok'tar Ogar!!!
*Alliance Victory*
Varian: Glory to the Alliance!
Tirion: A shallow and tragic victory, we are weaker as a whole from the losses suffered today, who but the Lich King could benefit from such foolishness. Great Warriors have lost their lives, and for what? The true threat looms ahead, the Lich King awaits us all in death.
Horde PvP Battle:
Tirion: The next battle will be against the Argent Crusade's most powerful knights! Only by defeating them will you be deemed worthy!
Garrosh: The Horde demands justice! We challenge the Alliance! Allow us to battle in place of your knights
Paladin, we will show these dogs what it means to insult the Horde.
Tirion: Very well! I will allow it! Fight with honor!
Varian: Fight for the glory of the Alliance heroes! Honor your king and your people!
*Horde Victory*
Garrosh: That was just a taste of what the future brings! For the Horde!
Tirion: A shallow and tragic victory, we are weaker as a whole from the losses suffered today, who but the Lich King could benefit from such foolishness. Great Warriors have lost their lives, and for what? The true threat looms ahead, the Lich King awaits us all in death.
Twins Encounter:
Tirion: Only by working together will you overcome the final challenge, from the depths of Icecrown come the Scourge's most powerful lieutenants, fiercesome Valk'yir, winged harbingers of the Lich King!
Twins: In the name of our Dark Master! For the Lich King! You will die!
Twins Death: The Scourge cannot be stopped!
Varian(If you're Alliance): Not even the Lich King's most powerful minions can stand against the Alliance! All hail our victors!
Garrosh(If you're Horde): Do you still question the might of the Horde Paladin? We will take on all comers!
Tirion: A mighty blow has been dealt to the Lich King, you have proven yourself as able bodied champions of the Argent Crusade! Together, we will strike against Icecrown Citadel, and destroy what remains of the Scourge! There is no challenge we cannot face united!
*Arthas appears to wreck the party, no sound files.

*
Tirion: Arthas! You are hopelessly outnumbered! Lay down Frostmourne and I will grant you a just death.
*Arthas mocks them some more I imagine and this is when he takes out the arena, and we go down below to fight Anub'arak*
Anub'arak: Mhhhhhhhaaaaa, our guests have arrived, just as the master promised.
Anub'arak aggro: This place will serve as your tomb!
Anub'arak death: I have failed you...master...