Gran Album Bridge/Grand Hall
Go downstairs, destroy furniture to obtain Red Orbs and go over the bridge. You will be attacked by new kind of knights - Alto Angelo. They're stronger than Biano Angelos. In Grand Hall, near stairs you will find Devil Star S and Combat Adjudicator (you have reach S level). There is a nasty trap in a next room - moving lasers. You don't have to jump over them - go to the entrance to the east side of the hall.
Key Chamber/The Gauntlet
Destroy knights and take Key of Cronus. This artifact will let you slow time. Use it and leave this room using entrance to the west. Activate the machine and go inside the cage. Destroy all enemies, go outside the cage and slow time - enter the cage avoiding laser. After destroying Frosts you will have the option to exit the cage through a second door and obtaining Blue Orb Fragment. In any case you should reach Statue and entrance to Angelo Agnus' room.
He is much easier than Credo - it's enough to attack him aggressively and when he loses energy use Buster (with Devil Trigger if possible).