Guys,
I will make an attempt at explaining. I have a Roadster and a GCX switcher. I also use a Rocktron Xpression in the loop for delays and reverbs. I switch them all using the GCX.
The Roadster has a bank of 1/4" jacks on the back to allow you to connect a switch (A basic on/off toggle) to control any of the following: Channels 1 thru 4, loop, reverb, solo, mute. The GCX Rack unit has 8 channels (the floor pedal has 12, but that is a story for later). I use an 8 channel 1/4" snake betweeen the GCX in my rack and the Roadster to connect channels 1 thru 4, solo,and loop. I don't use the reverb on the Roadster. I use one of the GCX channels to mute my tuner as well. So on the GCX floor controller I have 7 buttons to control on or off of each of these functions. Make sense so far?
Now for each of these channels there is also the capability to send Midi Program Change messages when you hit the button. These tell midi capable devices like the Xpression to change patches. I have the GCX send a change command to the Xpression to change to a slap back reverb on the Xpression when I hit channel 2, which I use for clean rhythm playing. I have it change to a nice full room reverb with some delay when soloing on channel four.
The floor pedal unit has 12 buttons. I use the balance (5 other buttons) to send CC messages. These are Continuous Controller messages (don't be confused by the name, they can be continuous as in a wah pedal, or simply on off) that can turn on or off certain elements of a patch on the Xpression. I turn on or off the Delay, Chorus, Compresor, Pitch Shifter, and Phaser. So within each patch I can get a higher level of control on the XPression and turn off or on certain patch elements.
OK - last thing. One or more of the 8 switching channels on the rack unit could be used for an effects loop for pedals if I choose to use it that way. I could put each pedal in its own loop and control them all individually (up to 8 obviously, provided I didn't use them for amp switching) or I could gang a few pedals together in one or two loops, as would be typical. I don't do this, but it is a common way to use these devices. I use the switcher to control the effects loop on the Roadster, as I said above.
Does this make sense? I know it can seem confusing. It was a scary day when I unpacked the GCX and had to think about all this, but it becomes pretty obvious once you have the stuff in your hands.
Here is a picture of the floor pedal:
HTH
Joe