You're asking a lot of different questions, here. Lemme see:
A500 you can add an accelerator to either the side expansion slot or by plugging into the processor socket. Trapdoor doesn't contain the necessary lines for an accelerator.
A600 is more limited - accelerator can only be added by plugging in "over top" of the CPU. It's surface-mounted, so no socket.
A1200 can take all manner of accelerators, bus board expansions (Mediator, etc.) through the trapdoor slot. Vampire is in the works, but since it's more complex AFAIK no ETA yet.
Hope this helps!
