This didn't work the way I wanted it to. But still, I got something good out of this.
Audio clips are provided at the end of the video.

Update!
I published a follow up video:    • 3D printed sound system - take 2  

STLs:
Case: https://v4.no/stls/AMPcasev34.stl
Cover: https://v4.no/stls/AMPcoverv34.stl
Backplate with 8 mm hole for DC-connector: https://v4.no/stls/AMPbackplatev34.stl
Backplate with 12,5 mm hole for DC-connector: https://v4.no/stls/AMPbackplatev36.stl
Feet (print in TPU): https://v4.no/stls/2xAMPfeet.stl
No stls for the speakers... (watch the video)

Electronics:
Amplifier boards: https://www.banggood.com/XH-M542-100W...
Speaker terminals: https://www.aliexpress.com/item/32871...
RCA connectors: https://www.aliexpress.com/item/40005...

+ suitable power supply (12V-26V) and chassis connector