Michael Wessel is the author of several hardware expansions for Amstrad CPC which I let you discover on his github and Youtube channel.

His last making is the MegaLambda-x6(++), an Amstrad CPC expansion backplante with no less than 6 slots. You can desactivate individually each connected card. It features :

• Six standard MX4 expansion slots
• Passthrough edge connector (like LambdaBoard I, II)
• Passthrough pin header connector (like MotherX4)
• Keyhole in edge connector for hardware that requires it (e.g., DKTronics Retro Speech Synthesizer, ...)
• Wide signal traces for good signal conductivity
• Extra wide traces for GND and VCC - unlike other backplane expanders for the CPC, MegaLambda is capable of powering the DDI-1 and DDI-3 without requiring an extra power supply
• Backplane powered from either the CPC or an external 5V power supply via standard barell jack (center polarity positive)
• Double jumpers (for better conductivity) to select between CPC power and external power
• Power LED (only) if external power supply is used - polarity check!
• The 5V / VCC line of the CPC expansion port is physically disconnected from the backplane if external power is used; only GND is shared with the CPC
• CPC Reset button

Several presentation videos are available :

• the initial presentation by LambdaMikel (see below)
• the second presentation by LambdaMikel of the upgraded MegaLambda
• the presentation of Manfred Gross's Amstrad CPC which is using the MegaLambda to connect the Ultimate Midi card (also by LambdaMikel), the RSF3 by TMTLogic, and much more !