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

Hi group,

in the Xl7 manual the following is stated for the "MIDI In Channels" 
parameter:

This menu allows MIDI data received at the MIDI input port to control
either the internal "A" or "B" channels. With this switch set to "B", you
could play an external MIDI keyboard on channels 1B-16B while channels
1A-16A remain dedicated to the internal sequencer.

How does this work exactly ?
I'm trying to use the XL7 with two external synths connected to the two MIDI
out ports. I need to play the synths while still be able to tweak and play 
the XL7
independently on all 16 tracks.

When set to "A" I can play the external synths but when set to "B" no 
incoming MIDI data is
passed to the output ports. Merge MIDI In to Out is selected for both A and 
B ports.

Please give me advice on how can I achieve playing independently on the XL7,
playing independently the external synths and being able to tweak the 
external synth
parameters (MIDI CC) on the XL7.

I'm confused, I think I'm misunderstanding something here ... I admit 
English is not my native
language.

Thanks in advance:
        Zsolt