AHA! I solved it!
Just in case somebody ever has this random problem-
I have a Soundblaster Audigy card installed, and my onboard sound is Realtek '97. I disabled my onboard sound. I also made sure to set my speakers, which are just two speakers with a subwoofer, to 2 channel instead of the default 5. I guess Oblivion's voice acting all tries to play through some kind of central channel.
So it was either the problem of having two sound cards on at once, or Windows 7 setting one's speakers by default to more channels than I actually had. Most sound worked fine, but Oblivion's speech in particular did not until I changed these two things. Had to go pretty deep into the control panel, configuring my speakers and sound card to do it, but luckily it has a nice user friendly "test" system.
So, that's that. Now I can hear all about freiheit again... :}