HomePod mini sound quality source

I have 2 HomePods mini in stereo.

My question is: Why so poor flat sound if you transfer sound from Iphone or Apple TV or iPad. But I have really great sound if source is iMac with activated EQ (Rock)

On iPhone a can choose this EQ too, but only iMac give great sound quality. I was searching info in the internet and YouTube, nothing. Who can discuss what I need to do to have such a good sound quality on transfer from iPhone and iPad like iMac?