So it works for me. I have an old Onkyo radio/receiver (without DAB, of course). I plugged the Digitradio 11R into the VCR/DVR cinch connection and by switching from radio to VCR I receive DAB+ and all other modes.
It works perfectly and the app is also convenient (via tablet/smartphone) to simply save all stations as favourites (instead of using the remote control supplied). Hope my answer clears things up! 😉

Don't be misled by the word "adapter"!
Do I understand correctly that you want to connect this device to an existing radio so that the existing device receives the DAB signals?
Then a clear no! It doesn't work like that!
Every DAB device is an independent tuner, even if it is called an "adapter". It has cinch outputs that are connected to a cinch input on the amplifier.
If your amplifier still has a free cich connection (high level, no phono!), you can simply connect it to it and use it
I don't know of a single tuner, whether consumer or high-end, that has any input connections.

Exactly, it also has a separate remote control.