Emu XL-7 & MP-7 User's Group

Hi All
Just joined the list, thinking of buying an command station but i 
have a few questions..
there are 4 simm sockets in the command station if im correct?
I gather that 3 of these cn5 / 6 / 7 are for the rom sound upgrades 
and one should have the rom that comes with the unit (XL / MP)
What is simm in the last slot cn8 for? Is this for user sequnce / 
program patch ram or used by the system?
Can you upgrade this for more storage?   
Thanks
Gonz