To play different music on different speakers, you should select each speaker in the Bang & Olufsen app and play music on it separately.
The Now playing page shows what content the currently selected speaker is playing. You can select other speakers by pressing the name of the speaker below the volume wheel which brings you to the expand screen and from there you can select another speaker to control by pressing on the speaker name. Once you have selected another speaker, you can control what that speaker should be playing.
Speakers can also be selected from the Home tab. Simply select the speaker and this one will be the one you play music from in the Now Playing window or from the Music or Radio tabs.