Yes. i will update after I get the Uno in there..  I may just keep the fcb at stock depending.....

Once you've got it all working, do come back and give us the details. Could be very helpful to someone else using those devices.

I figured out the FCB to gmajor and gmajor to Marshall and all is working well.   My uno chip will be here in 1 week.

After learning MIDI basics, start with page 18 of the G Major2 manual.
Page 14 of the JVM410 Manual shows the MIDI commands necessary for Channel Changing.

Find the section in each manual that explains how to set the MIDI Channels.
Set one device to MIDI Channel 1 and the other to MIDI Channel 2.
Any MIDI message TYPE can be sent on any Channel, but that setting is GLOBAL. PC1 will always send on Ch1 if so configured, CC1 on Ch 2 if so configured, etc. So, if the GMaj is on Ch1 and the JVM is on Ch2, then all messages destined for the GMaj will be on Ch 1 and all messages for the JVM on Ch 2.

Here's your first problem. The basic UNO configuration gives you 5 CC#s available in each Bank. Always the same in every Bank. While they can be sent on different Channels, my guess is that you're going to want to use them to toggle FX in the GMaj. Unfortunately, the JVM uses CC#s to toggle it's channels. It has 4 channels (4 CC#s) each with 3 STATES (called with the CC VALUES 0-2). That's 12 STATES. A toggling CC can switch between TWO States.

How to deal with this? I'm going to suggest that you use PRESETS on the JVM which call the correct Channel and STATE and plan your playing around that paradigm. 

An alternate plan would be to forget the UNO default configuration and treat the FCB as if it had the STOCK Chip. This would allow you to format multiple Banks as dedicated to the separate functions - one Bank plus two switches on the next Bank for JVM Channels, the other eight switches on the second Bank for GMaj toggle switches. Unfortunately, using the STOCK mode of the UNO chip will NOT track the LED Status for the Toggle switches. You'll also reduce the number of Presets you can call from 100 to 80.

Now what? You COULD step up to the UNO2 Chip. That would allow you to set any switch in any Bank (up to 199 Banks) to do whatever you want, plus have a dedicated Bank for toggle switches with LED Status tracking with one press access from any other Bank.

Unfortunately, now your homework includes not just learning MIDI, but learning the programming language required for UNO2 configuration. It's not just a simple GUI Editor. It isn't a difficult language, but I'm a former programmer. Do you have any experience programming in code? Also, consider the task of remembering what every switch does - just 100 banks x 9 switches is 900 things to remember in the heat of battle.

OR you could acknowledge the fact that the FCB is not really the right tool for the job (unless you're willing to devote a LOT of time and energy to the project) and start looking for the OEM controllers for at least one of your devices. My suggestion in this case would be to look for the JVM controller (as it will likely be a lot cheaper and easier to find) and use the FCB for the GMaj.

The problem there is - do you have enough real estate available for BOTH controllers?

Many owners of GMaj units really like them, I get that. And any device you already own is cheaper to use than buying a newer device. I've tried to give you the drawbacks of trying to use that venerable old equipment the way you'd like. I've encountered people who've moved up to a device like The Helix LT/Floor/Rack which has built-in programmable MIDI, then they put their GMaj in the FX Loop of the Helix so they can continue to use their favorite FX. At least, until they realize that there's only a couple of things that aren't in the Helix. Yet. Helix is an evolving plat form. The GMaj is... not.

Anyhow, lots to think about here. Any more questions, feel free to ask.

First, of course, you gotta learn MIDI.  Sorry, but even a cursory understanding put you ahead of most new MIDI users.  There are many MIDI intro videos on the web, but they all (IMO) suffer from info diarrhea - way to much crap info you don't need that only confuses and delays learning.  (One started off with Five Minutes of MIDI History, fer cryin' out loud.)  Find one that works for you, or study it on your own.  Maybe someone here knows of a better video I missed.

Some terms to look out for and learn well are Program Change messages and Continuous Control messages, abbreviated PC and CC, and MIDI Mapping.  PC messages are what will select patches on the G Major and the Marshall amp.  Each preset on the FCB1010 can send up to Five PC messages, so you can easily set both the G Major and the JVM with one preset.  Getting each of them set up to do that will be the fun part.  Both seem to have MIDI Mapping, which will make things a little easier once you know what you're doing.

Hopefully one of the other people here in the forum have experience with the G Major.  When you first start out, MIDI seems like a lot to learn, but it's not that bad.  Please feel free to ask specific questions when you have them.

I have had a G Major 2 for quite a while and know it but have never used MIDI.  I am seeking a write up guide for FCB1010 for using with G Major 2.  I will be using it mosly in stomp box mode but will also want the G Major 2 to switch my amp via MIDI (Marshall JVM).  Where should I start in terms of what docs to read and where to go?  I am very new to this "Groups.io" forum and not sure how to navigate.  Thank you!