The below voices go unused in the game:
Announcer: "You need to practice more"
I think this was meant to be used if you failed in the second bonus game.
Announcer: "Super Art ready"
In the actual game, whenever you fill up your super art bar, the announcer will say
"Alright let's go!" instead.
Alex: "I'm Ready"
Gill: "I am your God"
This is not used in the arcade version, as CPU Gill never uses the win pose where he would say this. But in the console versions, you can unlock Gill and hear him say part of this in the first bonus stage -but it cuts out before he says "God".
Gill: "Witness my life eternal!"
Ken: "Shippu Jinrai Kyaku!"
This should be used with Ken's third super art, but it isn't. He just makes a load of grunts whenever he performs it instead. It's stored under two separate clips in the sound test, one for "Shippu" and another for "Jinrai Kyaku".
Urien: "You've got no chance"
Twelve: "Shinryuken!"
The deal with this is that Twelve has a super art called X.C.O.P.Y. where he can transform into his opponent and can use any of their normal and special moves. Whenever he does a special move, his voice sounds weird with this garbling effect going on. For example, this is what Ken's Hadouken sounds like, this is was it sounds like when Twelve does it. However, checking in the sound test reveals that all the super arts have this effect recorded for them too! Perhaps Capcom originally intended the transformed Twelve to be able to use super arts?