Question I would like to be able to switch between amp channels on the Mark V and the various G-System Presets. How do I do that

In theory you can use 2 x Y-Split cables from the SW1 and SW2 outputs to the external switching mono jacks on the Mark V - However, many users report that they cannot access Channel . User experience show that the best solution is to use a RJM switcher - Amp Gizmo or Mini Amp Gizmo and a custom cable (available at RJM) RJM Music Technology, Inc. ph: (760) 597-9450 - fax: (888) 484-0829 We have extracted explanations from RJM correspondance with one of our user. This information is very useful to any user of  G-System and Mesa Boogie Mark V (so thanks to RJM support and to the user who provided the info). RJM has made a lot of testing with G-System and Mark V. The Mini Amp Gizmo, G-System and Mark V will work quite well together. You'll be able to program the Mini Amp Gizmo to automatically call up any channel, plus other features like solo, eq, etc. for each preset in the user bank of the G-System. You can watch the G-System/Amp Gizmo/Roadster video on RJM website , the process would be exactly the same with a G-System/Mini Amp Gizmo/Mark V rig. Because the Mini Amp Gizmo will plug straight into the amp's footswitch jack, you can't use the amp's own footswitch simultaneously. You will, however, be able to control every function on the amp that the footswitch controls, primarily as preset combinations (that is, each user preset on the G-System can call up a particular combination of channel, fx loop, solo, eq, tuner mute and reverb). With some additional configuration on the G-System you can also do some tricks like making the boost button on the G-System control the amp's solo boost, or making the G-System's reverb button control the amp's reverb. The other thing you'll need is a standard MIDI cable and a power supply. Sounds Great can provide you with an appropriate power supply, although any 9VDC output supply will work as long as it can provide at least 150mA of current. (The G-System power outputs provide 200mA total, so you could power the Mini Amp Gizmo, but not much else unless it was a pretty simple pedal).