Spotify is lossy mp3
Chromecast supports up to 192 kHz hi-res lossless. This is also the upper limit on Apple Music Lossless.
The only downsides are that
- Chromecast cannot (or poorly?) do gapless playback
- Chromecast was not designed for hi-res and the software implementation is slow, so hi-res chromecasting makes the streamer work harder, which may or may not be audible.
And you may want to check out this thread - search for Chromecast within the thread: