FKMA,
There is a lot of info and pictures on http://www.rolandus/RUG/ARCHIVE/SUM_97/
FEAT15_1.HTM/BG_A90.HTM

Nice pictures on http://www.rolandcorp.com/japan/products/mi/
A-90EX.html

Pictures of the Expansion Boards and Memory Card on

VE-RD1, VE-GS1 and M512E
http://pt.roland.dk/catalogue/cgi-bin/
prod-main.cgi

VE-JV1
http://it.roland.dk/catalogue/cgi-bin/
prod-main.cgi

I think that it will be hard to find editors, as the boards are almost non patch editable.
You have access only to performances ...

Regards,
Fernando Justo