>>535092387
It is possible, but very hard. I have 18 subs, and while definitely hard, getting 2 more is possible, as 2 pieces only have 3 rolls (but ATK% rolls as well). For more than 20 you need 5 rolls into AP on discs which is really unlikely but for the flat main stat discs still something you could build towards.

399 is doable. But it'd be REALLY good that's for sure.