Raspberry Pi 2 and 5.1 Sound: Hammy Technoid Talks - YouTube
5.1 channel analog audio processor - Hackster.io
Expansion Shield x600 for Raspberry Pi B+/2B/3B/4B - DFRobot
New home theatre box with surround sound using the Raspberry Pi - Raspberry Pi Pod and micro:bit base
5.1 channel USB Sound Card for Raspberry Pi and Computers - Robotools
Amazon.com: Raspberry Pi HiFi DAC Pro Hat ES9038Q2M Audio Card PCM DSD Lossless High Resolution Digital-to-Analog Converter Adapter for Raspberry Pi 4 3B+ 3B Zero w Zero : Electronics
Nvarcher I2S Coaxial Optical HDMI DAC Digital Audio Sound Card Expansion Decode Board DSD512 for Raspberry Pi 2B+ 3B 4B - AliExpress
X6000P SKU:EZ-0052 - 52Pi Wiki
Expansion Shield x600 for Raspberry Pi B+/2B/3B/4B - DFRobot