That is odd. Do you have the latest official patch installed, or is the version that was bundled the Game of the Year Edition? Those races share the same texture files, but the voices are different. Maybe you are having a general problem with the game processing sounds. What type of sound setup do you have, a separate card or on-board?
I have the latest official patch installed. I don't know for sure but I believe this is not the Game of the Year Edition. I have on on board sound card, but if it were a sound problem wouldn't I be having other audio issues? Aside from this voice problem, the game's audio has been flawless. Of all the audio in Oblivion, why would one set of voices be all that is affected?
I used Jauffree as one of my examples because A. his name was easiest to spell and B. he has unique dialogue that I wouldn't have expected the Imperial voice actor to have performed. The game acts like everthing is fine except one voice actor has been completely erased and MOST of his dialogue is now covered by another actor. This is why I thought it might be a legal issue at first, such as Bethesda having a lawsuit or something with that voice actor.
I'm now leaning more towards my disc being defective. If this is the case, what should I do? I've had it too long to return it to the store for a refund.