For streaming services, keep in mind that with the NL/ML Converter you can use the streaming services of ANY linked NL device. Therefore, instead of using an Essence or a Core you can use the least expensive NL device -- e.g., BeoPlay M3 or M5. You get the added bonus of having a speaker in a link room.
Adding a second-hand Airport Express to either the AUX socket of the BeoSound 9000 or the Line-In of the NL/ML Converter is a quick and inexpensive way to add Airplay. Using the Line-In of the NL/ML Converter has the benefit of sensing the music to automatically play through the connected speakers if you connect the speakers to the converter rather than the 9000.
I have a converter connected to BeoLab 3 speakers with a Google Chromecast audio streaming dongle connected to the Line-In. I have a Google Home Mini configured to use the NL/ML Converter speakers as the default music speakers. With this I can use voice commands to play desired music from Deezer through the BeoLab 3 speakers.
Also, if you have the speakers connected to the converter and add an IR eye to the converter, you have HUGE possibilities of mapping B&O sources to the BeoRemote commands. I can use my BeoRemote to control three BeoGram turntables, a BS9000, a BC2, a BM5, a BeoSound 2300, a BeoSound 4, Chromecast, and Airplay via Airport Express all through that NL/ML Converter's connected speaker using just one remote. Multiple converters are needed for this type of setup, though.