From the dvd, the hda and ac97 are for the jacks on the front of the drive, so if you want to plug headphone in plug the hda in, I assume your motherboard has hi def audio.
And the switches, just adjust the fan speed, I'm not sure if you'd want them on low/medium. Suppose you could run something like hwmonitor and have the fan switch to low, see what the temps are, then change the fan switch to medium/high, see if there's any real difference.
do they NEED to be plugged in though?