Connecting HomePod mini’s to amplifier

Any advise will be extremely helpful.

I recently purchased two HomePod mini’s for a studio apartment. I stream from an iPhone 12 Pro Max that stores all my music via VLC + the Home app. The problem is it's not as loud as I would like it to be. If I step outside my main space where it appears to be loud, I can barely hear it in the bathroom or outside my apartment window. Also, during the recent halftime show I connected the Homepod mini’s in stereo mode to my AppleTv it was horrible.

Not familiar with home stereos or how to set them up. I watched a few YouTube videos and is now considering purchasing an AirPort Express and amplifier to enhance the sound.

I struggling to determine how I will be able to control the amplifier. How can I set this up? Everything online seem to reference using an old speaker in addition to the homepod. The homepods are my only speakers. Any suggestions?