Hi guys, let me chime in a bit to advise my findings
I have a Avant Gen 1, a BV 14 (android), a A9, A6, Essence Mk2, and a BS1.
I see all of these products on the B&O app, so naturally i thought that i would be able to do everything with them, and that is not the case
When i set up the BV14, the Deezer app would not work in my country for some unknown reason so i deleted the app and re downloaded one through the Google store. odd, but it's B&O so nothing surprises me now.
I took all of these screen shots and photos of the BV14 and then i re-read your question. It is not about the joining of sources, it's about using the Horizon (in my case BV14) as a stand alone music player.
You can use it as a stand alone music player with your BeoRemote One, but you cannot use it with the app as a music centre.
I just tried on the BV14, i had music playing on the BS1 and i clicked join on the BR one = success
On the BV14 i also tried the app, with the BS1 playing and then "touch to join" on the app via the products menu = success
i put all products in stand by
i then pressed BV14 on the app (products menu), it says "waking up" - it did not wake up = fail
In the Beo app (music menu) and played on the BS1 i clicked the ... to expand to the BV14 - the 14 is not available in the ... menu but it is in the (products menu)
I went out of that, selected the 14 and then tried deezer and the message states "the selected product does not support playing deezer content" = is that because i deleted the deezer app or because it doesn't support it?
Findings:
- you can play Deezer on the BV14 via the BROne or other BV14 connected sources
- you can stream from other NL products to the 14
- you can select any source from other NL products on the app (eg from the a9, BS1 etc) and that will play on the 14
- you cannot select the 14 from the app and play to it
Hope this helps.