DCAudioDIY.com

https://www.matrix-digi.com/product/93/mini-i_4

Looking at this product. Can you use it on a simple network with no internet? This streamer, a computer with my music files (Windows7, Daphile?), and a switch if necessary?

Files loaded/saved on computer and the streamer to control playing.

It should work if your music files, controlling phone with app and the Matrix are all on the same network. Yiu just won't have access to any intenret streaming like Tidal or Spotify.