I've just registered to AA to share my experience with this setup, long story short, yes, it improves sound. (Denon 4700 + Node black.
Used RCA cables instead of optical, way better, setup Denon in pure mode, since the decoding is made by the Node's DAC.
I streamed Spotify, Tidal and Qobuz, also played from an external USB drive music files, DSD and Flac.
In every case, sounds better, difference wasn't that impressive when streaming spotify through the Node to Denon compared to Denon directly.
Mention apart is the benefits and simplicity of the BLUOS of the node when compared with one of the crappiest Apps out there..yes, HEOS.
In conclusion, if you enjoy the best from your lossless audio files such as flac, DSD and others formats, or if you stream from Hi Res services, such as Qobuz, Tidal, you will be benefited from the addition of the Node in your chain. (also consider the Node unfolds MQA files from Tidal, while Denon doesn't )
On the other hand, if you just want to stream Spotify, I would use streaming directly from the Spotify to Denon AVR in pure mode, sounds quite decent.
So it depends, always depends.