Hi Jean,
The A,B and C banks can be used in many ways. With the Expand filter on they can become 3 additional banks giving you 13 instead of 10. You can also use them along with the composer or factory styles. A set up I use is: after you set your styles and instruments in Composer transfer them to the 20 Custom Section, then load 3 different styles in Composer, then your 10 banks from the factory styles. So in effect you have 33 different banks of styles and regs and can play all night with only loading 1 file from the floppy. Hope this is of some help.
Best Regards,
Dave Shively