> The ST-V board has a multi-cartridge mode, but how do you add the additional
> carts? Are there other motherboards (like the NeoGeo MVS), a special adaptor,
> or is this another unused feature of this board? I haven't found any info on
> this feature other than it exists. : (
>
There is a version of the STV motherboard that has 6 slots, simple as that!

Six...

System16 - The Sega & Namco Museum