I have two which I am using in a TC Electronic G-System compact 4U rack bag. The G-System is great for a lot of things, but interesting and unusual effects is not one of them. It doesn’t even have a Leslie/Rotary effect for instance, and its harmonizer and tape echo algorithms are way worse than the H9s But I love it for its use and functionality, and other core effects sound great like basic delays, reverbs, and pitch up down. So I run one H9 in mono through one of the G-system’s front pedal loops, and a second H9 between the stereo outs of the G-system and effects loop return of my amp. This is excellent because it enables me to send an H9 effect into the front of the amp or the effects loop of the amp, use two H9 effects at the same time, and control it all with the G-System on a patch by patch basis with MIDI. It also enables me to vary the order of effects on a per patch basis. So for instance, sometimes I want my Vibrato effecting my delay, meaning effects order has to be Guitar > Delay > Vibrato > Amp. Other times, I may want reverb going into a Bitcrusher. Having the ability to pull an effect from any of three spots in the signal chain of H9 > TC > H9 is just super flexible, and at a minimum means I can have 3 effects in any order I want. Golden!

More info in case the above doesn’t make sense to you: 

The G-System is best used in a “4 cable method” kind of thing meaning that cable 1 goes from guitar into G-System “front end”, cable 2 goes from G System “front end” into amp input, cable 3 goes from amp effects loop send into G System “back end” input, cable 4 goes from G System “back end” output into amp effects loop return. This enables you to place and control effects with the G System in both the front of the amp and the effects loop. You would do this for instance because delay and reverb sound very different (and equally as interesting depending on what you’re going for) when put through the front of an amp versus the effects loop. The G System has 4 “pedal loops” in its front end where you can put whatever effects pedal you want in that loop, and toggle them on and off via loop control.

Very clever and effective.  Thanks for the explanation.