MP3@64 is an expansion sound module for the 
MMC64 card.  MP3@64 allows your Commodore 64 or Amiga
¹ to play MP3 music files at high quality.
MP3@64 uses a DSP (Digital Signal Processor) for MP3 decoding and a separate D/A converter in 20-bit resolution for high quality sound output.
The output can either be taken from the dual RCA connectors or a 4-pin audio connector.
Installation is staright forward- the module simply clips onto the 
MMC64 expansion.
¹ Amiga compatiblity is supported through third-party device driver written by Chris Hodges which can be 
downloaded here.  Your Amiga will require a compatible clockport to connect the MP3@64 hardware:

  Highway USB clockport

  Unity Prototype clockport

  X-Surf clockport

  ISDN-Surfer clockport

  VarIO clockport

  Buddha flash clockport

  Kickflash clockport