This is how I got my first shard A. Shantotto MB kill at least 10-15 mobs before it dropped. I use double light SC in every mob. I tried to replicate this yesterday with no success.
I was able to replicate Shupyrg's result (page 29) twice using 2 mules on PUP, each soloing Sortie separately. Both mules were making skillchains with the automaton (Dragon Kick > Armor Shatterer) and letting Shantotto magic burst.
mule1: PUP, Valaineral, Yoran-Oran, Shantotto, Koru-Moru, Monberaux
mule2: PUP, Valaineral, Yoran-Oran, Shantotto, Joachim, Cornelia
Both PUPs received the #A shard on the 8th acuex, and I didn't have enough time to try for the #A metal.
A few nights ago I was able to get the #A shard objective from an acuex in the south. After pulling the acuex and meleeing it for TP, I shoved a 96k Leaden Salute down its throat, and had only time to cast only two spells (Fire IV for 6624, Fire V for 7401) before Valaineral finished it off with a melee+enspell attack.
Tonight, I tried to use WarlikePatrick's Fireball to see if that would trigger the chest objectives, but I was not able to get to get either after clearing all 12 acuex in the north (including killing 5 at once). Fireball hit for 10k every time with this alt's decent pet MAB gear. Unfortunately I timed out before I was able to finish the entire south area pull with Unleash'd Fireball (~15k).
Also, I killed the Cachaemic Bhoot without aggroing any #C mobs, pulling the Bhoot with Provoke while it was just inside the Corse room. During the fight I magic burst 9 times (Fireball x3, Holy x3, Holy II x2, Dia x1) while making Fusion > Light > Light skillchains. The Bhoot died to damage from a Light skillchain (no opportunity to magic burst after) and DID NOT drop its red chest.
The Biune Porxie did not drop its chest, but I had killed no #B mobs and so this was not unexpected.