Audio Track:
On the 3rd and final disc, go to the "Extras" menu and click on Dimension tables. Highlight "The Real World" and press Left. The audio track will start playing, it's Makoto Mizuhara explaining the different worlds that they visit.

Bonus Feature:
Disc 1. In the main menu, place the cursor on "Enter the Magnificent World", go left and press enter. You will get a greeting by Rune Venus.

Audio Clip:
Disc 2. Enter the Setup menu, make sure that the English audio is selected and subtitles are off. Place the cursor on "Subtitles", go right and press enter. You will hear Jinnai rant.

Bonus Feature:
Disc 1. In the Extras menu, select "Also on DVD". On the screen with Fushigi Yuugi and Tenchi Muyou, go up and press enter. Nanami will then present the Magnificent World of Commercials.

Commentary:
Disc 2. In the Scene Access menu, go to the Sixth Night, place the cursor on "Opening", go right and press enter. The opening will play, with the cast commenting.

Commentary:
Disc 3. In the Scene Access menu, go to Episode 1. Place the cursor on "Opening", go right and press enter. The opening for OAV series 2 will play with the cast giving their comments.

Bonus Feature:
Disc 1. In the Extras menu, select the Art Gallery, and go to the 56th(!) picture. (This is a picture of the Springs of Arliman, in case you lose count, or I did.) Go up and press Enter. The four priestesses (including Kawoor!) will talk a bit.

Bonus Feature:
Disc 2. In the Extras menu, go to the Line Art menu, and select the Items. Go to item number 3 (Afura Man's lamp). Go up and press enter. Afura (I think) will talk about the priestesses' lamps.

Audio Clip:
Disc 2. In the Extras menu, select the DVD Credits. While the credits are playing go up and press enter. The credits will restart, but this time (a drunken) Fujisawa-sensei will rant about you reading the credits during them.

Commentary:
Disc 2. In the Extras menu, place the cursor on "Non-credit Ending", go right and press enter. The ending will play with Alielle giving her comments.

Bonus Feature:
Disc 2, enter the Scene Access menu and go to the Seventh Night. Place the cursor on "Encounter (Reprise)", go left, down, down, up, and press enter. Ifuriita will then ask us to take good care of our world.

Bonus Feature:
On Disc 3, enter the Extras menu and place the cursor on "DVD Credits". Go left, up, up, down and press enter. You will get a new menu that looks identical to the ordinary Extras menu. Here, from "DVD Credits" (again!) go left, down, down, up and press enter. The credits will play with the cast giving their thanks.

Bonus Feature:
Disc 3. Let the main menu play through to its end once, so it restarts the music. Press 5. You will get a picture of some caves, with a numeric keypad in the upper left corner. The digits in the keypad can be selected, but it seems to always return to the same picture again and again.