Hey guys!
I really enjoy playing with your software.
Got really frustrated at first, but it gets easier and it´s worth it!!
Anyway…
Got stuck here:
I´m on a Windows PC, controlling iTunes via powershell.
Hello,
I think it’s not possible for now 
No way to control airplay device using itunes and powershell but …
I use a workaround
Settings are store in %roamingFolder%\Apple Computer\Prefrences\ByHost
I make the configuration I want for the speaker and then exit itunes
I copy the preferences folder to Preferences_Bathroom\ByHost
When I want to start itunes with powershell, I stop itunes if running, copy the Preferences_Bathroom to Preferences and then I restart itunes
ex.:
Stop-Process -Name Itunes
copy-item ‘C:\Users\User\AppData\Roaming\Apple Computer\Preferences_SDB\ByHost*’ ‘C:\Users\User\AppData\Roaming\Apple Computer\Preferences\ByHost’
$iTunes = New-Object -ComObject iTunes.Application
$iTunes.SoundVolume = 35
Then start playing what you want
I did it for 3 differents Rooms
Problem… slow to start 