The correct combination is 2112 applied as follows...
1. Go to Disc 2 Main Menu
2. Select the #2 MX Multiangle song, "O Baterista" then back to the menu right after it starts.
3. Select the #1 MX Multiangle song, "YYZ" and then go back to menu after it starts.
4. Repeat step 3 again selecting the #1 song YYZ then again back to the main menu.
5. Repeat step 2 selecting the drum solo (song #2) and again go back to the main menu.
When you return to the menu "Anthem 1975" (which is the promo video from '75) will now be accessible.