I had to reboot about four times before the Dell drivers were able to finish the installation process - my system kept hanging at the point where it detects and installs the game controller port.
Once I finally got them loaded, it first played all sound through my PC speaker rather than my external speakers. I manually removed my on-board audio stuff from the device manager, and that helped with MP3's, but MIDI stuff still played through the PC speaker.
After I installed the TB drivers, it fixed everything, plus updated the speaker icon in the system tray (something the Dell drivers didn't do).