5??? and the cartridge itself has to feed them? I'm no electronics engineer but that seems like brute force. Are we talking audio and multiple sprite layers or is it more esoteric than that?
Does the PCB have to have so many layers because the network you built is made to match original hardware with separate chips for each bus.
Yes, indeed there are five busses that all have to be supplied data by the cartridge. That's why the Neo Geo carts are so expensive, large and have two PCBs. And also why the console was so advanced when it launched in 1990.
The five busses are:
V=8 bit PCM digital audio samples
S="Fix" graphics overlay for score, lives remaining, etc
P=16 bit programming code for the Motorola 68000 main CPU
M=8 bit programming code for the Z80 sound CPU
C=16 bit graphics data
Plenty more info for inquiring minds at the Neo Geo Dev Wiki:
https://wiki.neogeodev.org/index.php?title=Main_Page