I haven't played with multi-room much outside of wired solutions and Sonos, but Chromecast with iOS devices is a very slim-pickings deal. iOS is Airplay. That's what they build and design around, so if you are going to go for some wireless solution, in a iOS home, then you want to talk Airplay the entire way through the conversation.
Sony's support of Airplay looks like it is non-existent. Chromecast shows some support, but their main connection type is Bluetooth, which is not wi-fi based, and is often range limited for in-home use.
I would be looking towards a more comprehensive wi-fi solution for the home that comes from a company that actually focuses on whole-house audio. Sonos has been a class leader for a while, and there is a reason for that.
I can't even figure out what Sony is trying to deliver with their connected devices as they seem to be all over the place as to how it can be used with zero simplicity or direct focus in any area that they can explain.