It's been a long time since I played around with the Axiom settings and I have an older model so things may be a little different for you.

You set the Axiom Preset to 17 via the + and - keys in the numeric pad area (labeled 'Snapshot').
The display will show P17 or whatever.

Each of these is a different setup and Preset 17 is one that sends controller data the way most things that I use like it.

You can probably see the list of differences in the Axiom manual.

Enigma is the free M-Audio MIDI set up software that let's you do as much damage as you like to the MIDI controller stuff. You can download for free from the M-Audio site.

What you are calling channel is a bit confusing. MIDI has 16 channels and these are usually reserved one for each instrument (and 10 is usually a Drum machine).

The actual name is Controller number - 'Continuous Controller'  (CC) to be more precise - and there is a preset list of many of these - 1 is the Mod Wheel, 4 is a foot controller, etc. But you are pretty free to change these as you like. However, many things are already set up to recognize things like Mod Wheel data, so if you do change them, do so at your own peril.

Enigma lets you make your own presets of the Axiom settings - you can change zones, split the keyboard, change velocity curves, lots of stuff that I once played with but now forget completely.

I usually use a DAW for this and just use the Axiom as a keyboard with a few switches. Mod Wheel and Foot controller are my main external controllers.

Well, I have a Behringer FCV100 and a M-Audio Axiom 61 (first generation) and until today not had success for to make it work fine. But today I read a post on the Internet that saved my day.
The Control Change 11 (expression) is the correct one to be used, it is not the problem, but the Control Change 07 (volume) also can be used. I also had the range 60 - 127 with the FCC100, although in the Axiom 61 the Data screen 2 was setted to zero and Data 3 setted to 127.
Assuming you are using a stereo cable with P10 stereo plugs at each side, you need to invert the position of the positive and negative wire positions in only one of the sides of the cable. This really work, although seems very strange.
Now I have a 000-127 range of values when pressing the FCV100, and a very smooth transition of steps.
Try this easy step and be happy with this fantastic and cheap pedal.
Greetings.

One note:
I´m using the FCV  in CV mode for to control volume in the MIDI parts.
Best regards.

Sounds like the OP is confusing midi channel and cc number.  So, you can control volume with cc number 7, you can then set what MIDI channel you will be broadcasting on.... one way to know what channel you are using is to set the INPUT to your AXIOM and a specific channel number... if you get NO DATA, then the AXIOM isn't broadcasting on the channel you set in SONAR.....  play around... get the MIDI channel working and then play with the settings for controller data.
 
Just an idea to help you,
Jim