On Serdashop you can found audio and video cards to be used mostly on PC. For example there are two cards which are connected to the parallel port of a PC, especially those which can't use ISA/PCI sound cards such as old portables :

• OPL3LPT which uses a Yamaha sound chip : OPL3 which you can found in many msdos sound cards starting with the Sound Blaster Pro 2.0). You can see the OPL3LPT being used wit the Police Quest 3 demo
• S2P, which permits to use General MIDI. MIDI was at msdos time the best sound ever, but MIDI expander were not cheap. You can see the S2P with the game Betrayal of Krondor (nice music)

Pulkomandy has created a card for Amstrad CPC(+) : Willy which lets you use an OPL3LPT or S2P on it. He wrote two programs to use the OPL3LPT which you can found on his page :

• SA2 Surprise! Adlib Tracker player by Madram
• VGM player by PulkoMandy (uncompressed VGM at the moment)

Check the CPCWiki thread for more informations and short videos of the Willy + OPL3LPT being used.

By the way, there are other ways to use MIDI on an Amstrad CPC, but it will be for another day (hint, use serial, usifac, LambdaSpeak...).