When playing Spotify Connect volume keeps changing between songs. When streaming in connect mode the setting "Volume normalisation" is not available. From what I can see on the forum the same problem when streaming over chromecast.
This should be fixed , it is very annoying having to change volume all the time.
When streaming with Spotify Connect, certain playback settings will not be available. Look in the settings for the device you are streaming to instead. You could try for example to disable Full Dynamic range. Here's how.
Hope it helps! Let us know if you have further questions.