SN 54.2 is a dubious and ambiguous sutta with no parallel.
I wish I could find “ānāpānassatisahagataṃ satisambojjhaṅgaṃ” in a sutta with parallels; and in which context.
Sorry to be a downer again.
It’s the citta - it’s all in the new (internal) citta - the partially liberated citta.
The internal dhamma is the making up (with the mano, ) of the body/breath, (then) the experience/feeling from that breath, (then) the new (internal) citta, so to speak.
It is about training with the help of the breath, until one liberates (partially) the citta.
The dhammavicaya ( 13th step of anapanasati,) comes after the release of the citta.
It is about training to breathe, to perceive (anupassi) the “foreign nature (not-one’s-owness)” of the external dhammas, in relation to the mano builded dhamma.
The knowledge of such a release is the knowledge of the anicca (not one’s owness) of the (external) dhammas.
In other words, the nature of this newly liberated citta, which can be attained only through an internal dhamma, helps one to understand the not-one’s-owness of the external dhammas - their conditioned, dependently arisen, subject to destruction, vanishing, fading away, and ceasing nature. The same way that this internal dhamma is somewhat conditioned and dependently arisen from body/breath, feeling and citta - and is subject to destruction, vanishing, fading away, and ceasing.
In other words, understanding that the internal builded dhamma leads to a liberated citta, makes you understand at least, the not-one-owness of the external dhammas.
In other words, when you make your own hamburger, you can understand better what McMickey is all about; and your spirit is alleviated. A much better and freer spirit.
And you can sambojjhange your spirit away on that new own hamburger, in relation to the other(s) 
.
Now the later dhammavicaya sambojjhango (the fulfillment/paripuri of the preceding,) is about discriminating (viharati) that dhamma with discernment (panna).
Anicca in the anapanasati step is not “impermanence”, but “not-one-owness”.
The other meaning of nicca in Sanskrit (nitya).
In fact, both meanings, viz. impermanence and foreigness, are closely related, as you can see.
As I already mentioned, the arising is primarily the arising of the nidanas (the cause) ; not the arising of the dhammas per se.
This is the process of ending the “this is mine” part.
However, the new internal dhamma, as the “I”, must also be ended.