Thanks for writing in!
I would recommend looking into our SoundTouch 10 speakers HERE. They are great additions to the setup as they can connect wirelessly to the network to group with the Wave SoundTouch IV. One thing to note, you will not be able to re-broadcast the CD and AM/FM audio from the Wave system. The grouping feature was designed for services from the SoundTouch app and Bluetooth.
Tony A - Community Support
There would be two ways to approach this. You can still use Spotify to start the audio on one speaker, and then use the SoundTouch app to send audio to the other speakers on the network. The other way would be to open Spotify within the SoundTouch and control it all from there.
One thing to mention, the master speaker where the stream starts, should be the speaker with the best connection to the router. This can be checked under the RSSI values in the about section of the app for each speaker.
Let us know if you have any further questions!