There are 9 sphere benefits one can recieve, 6 from bodies (STP, MAB, CRIT, DA, HASTE, FASTCAST) and 3 from atmacites (REFRESH, REGEN, REGAIN).
There's no overlap between bodies and atmacites. Thus it's only with atmacites that one may be able to achieve a stacked effect. However you can only receive the benefit off the person with higher leveled atmacite should two people have the same one equipped.
Also sphere effects will only stack with atmacites that you have equipped that effect only ou. Eg Coercion + Promises... hope this helps.
== FOR REFERENCE ==
Here are the 6 bodies that have sphere effects:
1.
Fazheluo R. Mail: STP+6
2.
Anhur Robe: MAB+5
3.
Mextli Harness: CRIT RATE +3
4.
Mekira Meikogai: DA+3
5.
Toci's Harness : HASTE+2
6.
Heka's Kalasiris:FC+5
Here are the 3
atmacites that have sphere effects:
1. Atmacite of Devotion: REFRESH+1 (levels: 1, 5, 10), +2 (level 15)
2. Atmacite of Exhortation: REGEN+1 (levels 1, 5), +2 (level 10), +3 (level 15)
3. Atmacite of Promises: REGAIN +1 (level 10), +2 (level 15)