The AMZ inverts the phase, but judging by your description either circuit will be out of phase in their rig when used independently.
In order to make it work in their rig, you would need to add a phase inverting stage in series with each circuit. That way neither circuit inverts phase and they can be used independently or together without issues
This can be done a few different ways, but if you don't want to add another gain stage to invert phase, you can use an inverting buffer like the one at the bottom of this page
http://www.muzique.com/lab/buffers.htmOf course you could use a dual op amp to do both buffers with one IC