Order of Some Indo-Iranian Sound Changes

As we know, in the course of the evolution of P.I.E.
into Proto-Indo-Iranian the palato-velar stops became
palatal or pre-palatal affricates, which subsequently
developed fricative allophones before dental stops, so:

k^
g^
g^H
k^t
g^d
g^dH

became

c´
j´
j´H
c´t = [s´]t
j´d = [z´]d
j´dH = [z´]dH

In another change /s/ and its allophone [z] develop
palatal or pre-palatal allophones after /r/, /w/, /k/,
or /y/, RUKI, with the resulting allophones merging
completely at some point with the fricative allophones
of the affricates, if not identical to them from the
start.

Is it known, or is there any way of knowing, which of
the changes came first?

David