I'm looking for inexpensive AirPlay music streamer with a display able to show album artwork of the song being played. Only coaxial or optical output is necessary. I need something like Primare Prism NP5 but with a display and "turn off" switch. ...
If you are comfortable with using Raspberry Pis, then software such as Kodi can act as an Airplay receiver (audio only), with a USB connection to an external DAC.
As for the display, you somewhat have to "roll your own". The way that Kodi and the Linux graphics stack work these days, Kodi takes over the Pi's HDMI outputs (both of 'em if using an RPi 4). A second RPi, even something low-power like an RPi Zero, though, can be used to drive a display. That's the approach I'm now using with
kodi_panel
https://github.com/mattblovell/kodi_panel#readme
(Disclaimer: I'm the primary author of kodi_panel.)
I didn't originally intend to have two single-board computers for this setup. I started out with a SPI-attached LCD display driven directly by an Odroid C4 that was also running Kodi -- a nice, single computer setup. I kept hankering after a larger, IPS-based display, though. Such larger displays are typically HDMI-attached, so down that road I went. My primary use case is using JRiver Media Center (on a PC in a different room) to host the music files and use the RPi + Kodi as a DLNA renderer. Kodi can receive Airplay audio, though, so I occasionally listed to a podcast or two sent from an iPad to the RPi. Getting Airplay album art displayed from Kodi took a little figuring out, but it does work.
Also, one doesn't
have to use Kodi. I think Moode Audio and Volumio can also drive local displays (basically using X Windows and a web browser to show the same display page as their remote GUI). If this approach is intriguing, but you don't want to mess around with the hardware directly, Audiophonics has a few RPi + Display units that they put together.
One example is this:
Audiophonics RaspDac Mini LCD Kit DIY Streamer
[Edit: spelling, modified URL to point to Readme file, added Audiophonics link]