Configuration for AirPlay

[Delhayek]

Hey guys,

I'm about to buy a Devialet Phantom + Dialog but I would like to have more certitude about my (stable?) configuration.

I'll mainly listen my music with Spotify on my iMac, trough AirPlay (to avoid Sparkle, am I right?).

I'm not sure about the setup and have 2 questions :

1)
iMac ------ ethernet ------ Router ------- ethernet -------- AirPort Express ------- optical -------- Dialog

or

iMac ------ ethernet ------ Router ------- ethernet -------- Dialog ------- optical -------- AirPort Expres

2)
Is the connection between Dialog and Airport Expres in optical AND ethernet, or only optical?

Thanks for your help.