How to control external MIDI multi-timbre device

Question

I have an external midi device that has distinct buttons with which I can control on/off individual sounds. The device has a single midi channel but many different sounds that can be turned on/off in any combination - i.e., I can have two or more sounds turned on which the device mixes down to its stereo outputs.
Each specific sound has a name and can also be controlled with a midi message in the form of "Bn 49 xx" (on event) or "Bn 4A xx" (off event). I would like to be able to control these sounds from logic pro.
Note that I have refrained from calling these "sounds", "patches". A fundamental difference between a patch and a "sound" as I described above is that you can only select a single patch at the time - I need to be able to turn on/off any combination of these sounds.
Hope it is clear to someone what I am trying to do... your comments are most welcome.

Answer 1

After some serious support from Pancenter (thanks again!), I arrived at a working configuration using Apple’s Environment editor. In the hope that my learning experience is of use to someone else, hereby a quick write up.
My objective was to control the stops (programs) of two pipe organ modules from Logic Pro 9, preferably with a nice graphic interface.  The modules are broken up into 3 sections that each have a direct midi channel. I already set them up on my midi controller and could play a midi file on them just fine but not the stops. Rather than a typical synth program switch, stops on an organ can be turned on/off in any combination thereby mixing the sounds together.  The documentation I had showed these midi byte sequences for turning on/off a stop:
Bn 49 rr  = stop on
Bn 4A rr = stop off
with ‘n’ being the midi channel, and ‘rr’ the hex code for a particular stop.  With Pancenter’s help, I started playing around with a Fader/Button 3 on the “Click and Ports” layer from the Environment (command 8).  A button can be used to send a variety of midi message types, in my case I need a Control message with its channel set to the appropriate midi channel of the pipe organ module (channel 2 for me).  A midi control message has the form <control byte> <byte 1> <byte 2>. The byte 1 field holds the specific control and byte 2 the value for that control.
Buttons send their max value when on (depressed) and min value when off. i.e., the value of byte 2.  As you can see from the midi sequences listed above, this creates a bit of a complication in my case because the value ought to stay the same but the control (byte 1) must change.
I decided to set the button values to the midi stop I wanted to control as the min value and the max value as the stop +1. So my button out going sequences are now:
Bn 74 34    stop off
Bn 74 35    stop on   this should be changed to Bn 73 34
(Notice that 74 = 4A hex and 34 = 22 hex)
Using a transformer object right after the button, I detect the Bn 74 35 sequenc and change it to the desired Bn 73 34. As it turns out... easy as pie when you get a little help from a friend ;-)
This is the button with output to the transformer:
The inspector details for the button:
The transformer setup:
The entire pipe organ module with stops, just need to clean up the names a bit and we're done. Notice that I used a fader text object for the stop headers.
I am a 2-3 week user of Logic Pro and must admit that I am starting to be thoroughly impressed with its capabilities. The Environment editor is ahhwwsome though perhaps a bit daunting at first.   Thanks again Pancenter for your totally cool help !