It's quite possible that the new Hitachi is, indeed, not compatible with OS9. The only way to know for sure is to install OS9 for it 'for real', rather than by cloning... but since they haven't exactly been going all out to write OS9 drivers for new hardware (understatement
), I think guessing that it's not going to work might unfortunately be accurate.
Good tip re: "x" boot. Note that this will choose the first available OSX bootable drive: be aware that this might not necessarily be the one you want! Holding down Option will give a bit more selection, should that be something you need.