The only difference should be that the EII+ has double times the
memory as the normal EII.
This provides access to two complete banks (disks) in parallel.
You can't access both disks simultaniously though, but by pressing
"00", you should be able to switch between the two, without any
loading or something.
I do not own an EII+, but that's what I know about the +.
The message you got probably demanded an entry whether you want to
load the second bank from drive 1 or 2.
Greets,
Elm.