Hey myles,
I'm working on a dual extruder upgrade to make use of the E3Dv6 hotend, which provides much better performance and print quality, for the gMax. A few people are already interested. Essentially it's a custom cart to replace the one that moves left to right on the gMax carriage, and onto it you can attach 2 or even 3 toolheads of your choosing. Of course, if you want to go with more than 2 nozzles, you may be interested in the E3D kraken (4 nozzles). I'd love to set you up with a custom solution that uses it.
I have this setup running on one of my other printers very reliably and am using it on other printers as I build them.
I haven't posted any pictures of this publicly yet, but please do reply back or message me if you are interested.