Just confirming that. Even if you did manage to fit a ATX plug to the motherboard and connect the picoPSU to it, you still need to find somewhere to put the adaptor unit within the case.
Im not a great fan of having multiple stages of voltage conversion one after another (As with the picoPSU) - It all seems wasteful and reduces the overall efficiency of the system (A lot of their efficiency figures are >95% ... Id like to see some evidence...). Id opt for a miniure PSU if possible that provides the +5v +12v and -12v rails straight from mains (Just bear in mind that whatever option you choose, depending upon where you locate it, you may find yourself severly restriced for certain types of upgrades)
Hey, what are you actually looking to use the A1200 for anyway?
Hodgkinson.