Here is what I would do with this setup...
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You can switch between the three amp channels using only two loops, I showed it with Loops 7 and 8, but you can use any two loops you want. So in this example if Loop 7 is On (Loop 8 Off) you will get Channel 1, if Loop 8 is On (Loop s Off) you will get Channel 3, if both Loops 7 and 8 are Off you will get Channel 2. Judging by your current setup I'd have to guess that you aren't turning any GCX Loops On which is why your amp is staying on Channel 2.
On the Ground Contro Pro you will need to go into Setup Mode and activate GCX #1, and name the G-Major as a MIDI Device.
1. Go into Setup Mode by pressing both Setup Buttons at the same time.
2. When the screen changes, press the Expanders Button.
3. Set GXC-1 to On using the Data +/- Buttons.
4. Press the Device Name/Channel button.
5. For Device 1 enter "G-MAJOR" using the Data +/- Buttons and the Cursor Left/Right buttons.
6. Press the Cursor Right Button until the Channel Number is flashing.
7. Set the MIDI Channel to whatever the G-Major is set to respond on. (01 is the default MIDI Channel for the G-Major)
8. Press the Cursor Right button again to get to the next screen.
9. Set the "Starts At" number to 01 using the Data +/_ buttons.
10. Exit Setup Mode by pressing either Setup Button then press the Yes button.
This will get yo ready to start creating presets that recall sounds on the G-Major as well as set whatever combination of the GCX Loops you want on. Look to the Edit Preset section of the Ground Control Pro manual. Assigning MIDI Program Changes shows how to set what numbered patch you will recall on the G-Major, and Controlling the GCX Guitar Audio Switcher will show you how to set the appropriate GCX Loops to get the effects and amp channels you want.
Let us know if you get stuck!
p.s. Uploading pictures can be done by using a hosting service and posting the link, or by uploading a picture file when you are creating a post using the "Upload Attachment" panel under the "Post a Reply" panel. Once you upload a file you can use the "Place Inline" button under the text box in the "Post a Reply" panel.