the two gameboys on the left have been retro fitted with super gameboy CPUs. i took the original CPUs out and soldered in the new ones. the original idea was so that the gameboy can boot the snes, which is does but the bonus feature is a quick and silent boot.notice how the two gameboys on the left have booted the cart before the gameboys on the right have finished scrolling the nintendo logo.this gives an advantage when using the gameboys to play music live as you can switch carts without having to turn down the sound to hide the boot noise, and the cartridge is almost instantly loaded in the case of LSDJ it is loaded instantly
via YouTube
You still have to probably turn the mixer pot down to avoid the power PUMP when you power cycle the Game Boy. DMG line conditioner mod? Soft reset switch?