I've observed my tone loses a bit of gain or gets colored (a bit) tone with the FCB1010 connected. (volume pedal maxed and configured "post stomps").
Can someone try this?: set a hi gain profile, play some chords and palm muted riffs, disconect FCB and play it again. Are you getting the same tone loss than me?
PD: sorry for my english... 
you need to calibrate your FCB pedal. If there is less gain when the FCB is connected it means that the pedal does not send the maximum value although it might look like it is pushed all the way down.
The expresion pedals calibrated. And the tone suck persist.
Maybe it's not calibrated the correct way?
How did you do it?
have you tried to position the pedal post effects?
Does this "problem" appears in every rig/performance?
Did you change the position of the volume in the signal chain?
in the post effect position the volume pedal only controls the master volume. If you hear a change in sound it must be your monitoring system. Have you checked the headphone output?
How many stomps and effects do you have engaged?
Is there a wah stomp installed?
