pairing HomePod mini with Homepod

No, you can stereo pair two original HomePods (2018) or two minis, but you cannot mix and match.

As far as I can tell Dolby Atmos isn't supported on HomePod. See About spatial audio with Dolby Atmos in Apple Music - Apple Support for details of where this feature is available.

tt2

You can’t create a stereo pair with a HomePod and a HomePod mini.

You can create a stereo pair with two HomePods or two HomePod minis

Set up HomePod stereo pairing - Apple Support

You might get something that sounds nice if you set the volumes correctly, but it won't be true surround sound, just a mono speaker in the same room as a stereo pair.

tt2

Good info!