The goal of the project is to use the raspberry pi as a proxy for local devices (particular smartphones) to let them play their music on a stereo. A requirement is a high responsiveness. Playing media from USB etc. is not needed.
For that purpose, the raspberry pi is connected on one hand via 3.5mm jack to stereo (aux in) and on the other hand wirelessly to local network. I'm aware of raspberry pi distros like Volumio or RuneAudio but I'd like to build a system that is stripped down to the essential parts in favor of performance/responsiveness (e.g., no web interface etc).
As far as I know, UPnP/DLNA exactly provides the required functionality. However, I'm a bit confused about the terminology. As far as I understand, the simplest solution is to use a software that just acts as a 'DLNA renderer'. Local devices then can see the Pi as rendering point to which they can stream their music, i.e., the 'raw audio stream', to. Other devices have no possibility to control the stream (like skip to next song) despite streaming their own (raw media) stream.
The second solution would be to install a 'DLNA server' in addition to the renderer. Then, local devices provide information about their local media to the server, as well as instructions about what media to play from where (for which the devices need a 'DLNA controller', not the Pi). The DLNA server then advices a certain device to play particular media. Other local devices are able to skip songs etc.
Did I understood that correctly?