Korg Poly800/EX800 Users

hey everybody,

i've spotted a korg mex-800 memory expander up for auction.  i'd 
never heard of these things before - but looking at this one, i 
assume it works via sysex.  the only confusing thing is that the 
seller suggests in the auction listing that it will work with a poly-
800 mk1...  just wanted to check - is this misleading info, or is 
there something going on that i'm not aware of?  i know mk2s have 
sysex capability, but not mk1s - unless there was some kind of device-
specific compatibility programmed in..?

any help would be appreciated.

-gareth