The following is a general guide..

As you may or may not know you can re-map the Korg controls by
going to the MIDI|Parameters Mapping|User section. Refer to pages
30-32 of the English manual for an overview.
In this Korg menu you may freely assign MIDI channel and
controller numbers to all of the Korg's programmable parameters.
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Before you get started you pretty much have to define what role
the Korg will play in your studio.  (Keep in mind that you will be
altering only the USER parameters so you can always switch back to
the default system(s).)
The reason you should decide is that the controller and channel
numbers you will assign to faders etc. may already be used by
other MIDI controllable functions of the Korg.

Decide:
Method a)
If it is just going to be a MIDI control surface and nothing else
(just MIDI In/Out hooked up) If this is the case... it's a no
brainer.  You don't care about how you map the faders or what
functionality you lose when you 'steal' the controllers.

Method b)
If you want partial midi controller and some functionality (some
audio mixing and effects etc) Then you have to plan.  When you
'steal' a channel and controller number during the re-map process
you will break a function somewhere else.  You will have to re-map
those functions you broke.

An example..

You want to assign faders 1 thru 4 to control volume on MIDI
channels 1-4 in your sequencer program. You don't mind giving up
those faders but would also like to pretty much have the rest of
the korg work as usual.

In the USER map you would set:

Fader# 1 to ch# 1, controller# 7  (MIDI ch 1 volume)
Fader# 2 to ch# 2, controller# 7  (MIDI ch 2 volume)
Fader# 3 to ch# 3, controller# 7  (MIDI ch 3 volume)
Fader# 4 to ch# 4, controller# 7  (MIDI ch 4 volume)

Your results--
Method a) As a MIDI surface controller you're done. You don't care
about conflicts.

Method b) You are now conflicting with other controller
assignments as follows.

Fader# 1 ch1,cntl 7 conflicts with Fader# 8.

Fader# 2 ch2,cntl 7 conflicts with Korg channel 8 assignment to
Group 1.

Fader# 3 ch3,cntl 7 conflicts with Korg channel 8 assignment to
Group 7.

Fader# 4 ch4,cntl 7 conflicts with Korg channel 12 EQ mid level
control!

You have to remap the controls you 'stole' from to get their
functionality back.
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Keep in mind that when you ride those first 4 faders now.. your
Korg channel volumes will be changing also. Don't assign audio to
them.
You can remap the fader buttons MUTE and SOLO to send controller
messages and remap the PAN controls (send MIDI controller #10 to
pan your midi channels).

Unless you have a 'device' that can change it's EQ with midi
controller mesages.. there is no MIDI EQ.

ps: If you scootch your mixer.. go through the archives and see
Cris's reset procedure.  It's probably not a bad idea to do a
sysex dump and back up the board.

pps: If there are points you don't get here.. post back.

Rich
gorDesign solutions