roon basic setup recommendation.

[struts]

@struts
The extra functionality the Cubox offers is an optical connection to the Phantom (for hi res streaming) that is physically separate to your Roon Core

Just to simplify.
1. Roon core on laptop.
2.cubox to devialet spdif.

Now the Devialets are on wifi.
The roon core are on wifi too.
And the cubex on wifi.toslink to phantoms.
Will i be able to stream 24bit when there no direct input of the media source to the phantoms?

Almost.  I am unsure whether the Cubox wifi antenna will be up to hi res (it is a very small internal antenna).  You would have to try it, since even if it worked for someone else it might not work for you.  If it doesn't provide the coverage you would need to wire your Cubox to your network. So:
Now the Devialets are on wifi. - Actually now they are connected via Toslink to the Cubox which is connected to your network.  They can also still connect to your wifi for AirPlay of course.
The roon core are on wifi too. - Yes, that's fine.
And the cubex on wifi.toslink to phantoms. - Cubox wifi or ethernet depending on whether it can get a good enough wifi signal to support hi res.
Will i be able to stream 24bit when there no direct input of the media source to the phantoms? - Yes.  That is the whole advantage of this setup.