This is pretty straightforward. Incidentally, I had one of these for almost a year, and it worked great, though we never used any of it's MIDI stuff. It was our first digital mixer, and the church liked it so much they upgraded to the X32 Rack.
So, first you have to note that the Faders, Mutes, and Pans are A.) all on different MIDI channels, and B.) all controlled via CC values. This requires some planning, because of the way the FCB sends MIDI. It can technically send CC (Continuous Controller) messages on four different channels, but those channels are set up GLOBALLY - You cannot change them without reprogramming the FCB1010. CNT 1 and CNT 2 can each have their own MIDI channel, as can each Expression pedal.
A little clarification if you aren't familiar with the FCB's MIDI setup. If you are, go to the next paragraph. Each Preset on the FCB can do ten things when it's pressed. 1-5: Send five PRG CHG messages. 6 and 7: Send two CC messages labelled CNT 1 and CNT 2. 8 and 9: Set up the two expression pedals (including their CC#, min value and max value), and lastly, 10: Send a Note message.
CNT 1 and CNT 2 can only send one value each. If you set CNT1 to send CC# 31 with a value of '00', it will mute MainLR on the XR18. However, if you set Both CNT1 and CNT2 to the same CC# with whatever values, instead of sending two CC messages with different values, it will TOGGLE, sending the CNT1 value the first time you press it, and the CNT2 value on the second press. Perfect for a MUTE button. So in GLOBAL setup, set CNT1 and CNT2 to both use MIDI channel 2.
The Expression pedals are what you want for the Fader group. so while you're still in GLOBAL setup, set EXP1 and EXP2 to use MIDI Channel 1.
To set a Preset to Toggle the Mute for a mixer channel, you set the value to '0' for mute, and '127' for unmute. In the example from above, with CNT 1 set to CC#31 and value '00', if we also set CNT2 to CC# 31, but value 127, you now have a Mute Toggle.
Next, setting the Expression pedals. The CC#s and values for the Expression pedals are set by a Preset. For example, in that same preset, set EXP 1 to CC# 0 (zero) and EXP2 to CC# 31 and set the minimum and maximum value to 00 and 127 for both. Save it and exit. Try the expression pedals - they do Nothing!!! Remember, you have to select a preset (preferably one you've programmed!) to get the expression pedals working. So you hit the footswitch you just programmed. Now try the pedals again, and you'll find the right expression pedal controls Master Volume (CC# 31), and the left controls the volume for channel 1 (CC# 00). Hopefully... If not, try programming it again.
You can have the Preset set up the Expression pedals AND send a Mute on/off at the same time, but make sure you know what you're sending. For example, you could set up Preset 1 to mute Main LR and set up one of the expression pedals for Main LR Volume. Just remember when you press it the first time, it will mute MainLR (if set up the way I did above), and then the Volume fader won't matter. Well, it will matter - the fader will move, you just won't hear it until you unmute it by pressing the Preset again.
One oddity - what I called Min and Max for the Expression pedal values is actually a misnomer. Those values are actually called "closed" (heel down) and "open" (toe down) by Behringer. Why do you care? Because the closed value doesn't have to be less than the open value! e.g.: Set one pedal for main volume normally, and then set the other pedal to AuxLineIn volume (CC# 16), but reverse the values. Yes, that is a legal setup. Now if you fat foot it and move both pedals up (open) at the same time, you'll turn down the AuxLineIn at the same time you're turning UP the MainLR volume. Crazy! :-)
That should be enough of an example to get you going. Have fun with it.