I am successfully using the zaxmote with 4 of my transmitters. Same set up as you described. I took a day to go through all of my software updates and make sure everything was up to snuff. I need to add some more units to this set up next week for a job I am doing.. I will pay close attention to the settings and report back what I learned.
Off the top of my head.. The QRX/QIFB has to be set to bluetooth not serial port. That was a killer for me that is not explained anywhere. I just stumbled upon the setting and changed it.
Rem Ctrl Group ID can be uniformly=1 (or whatever) but your item code (? can't remember what exactly they call it) has to be numbered separately per unit 1,2,3..etc. transmitter 1 is 1 transmitter 2 is 2. and so on.
Lastly the thing I was screwing up was the TRX IFB (zaxnet transmitter) ON setting. I found by turning the transceiver off (which was kind of tricky to do-I can't remember what the steps were)..I was able to just focus on receiving the Zaxnet commands. The only reason to have a TRX transmitting IFB is to remote test the quality of the audio with a ERX which I would not have to do. I found that my individual transmitters set to individual Zaxnet frequencies were transmitting bursts of audio on start-up and were interfering in my remote roll commands for other transmitters. This is probably in part because of poor product knowledge and frequency planning on my part. Once I eliminated the feature everything worked great.