Good stereo setup for an A body?

Eliminate the head unit entirely and spend that money on a DSP(Digital Signal Processor) with built in amp instead.

Instead, download Tidal onto your smart phone for CD quality and above music streamed directly to the DSP and then to your speakers.

If you conceal the speakers, no one will know you have a very nice system by looking at the interior of your car.
Would I be able to stream an app like Spotify to the DSP? (that's where all my music comes from)

How does that work?

How many channel DSP would I need?

Sorry for all the questions!