Turn on IA Cycle for the button, then set up your actions like this:
H9 Bypass / off:None on:127
Mobius Bypass / off:None on:127
System / Step
H9 Bypass / off:None on:127
Mobius Bypass / off:None on:0
System / Step
H9 Bypass / off:None on:0
Mobius Bypass / off:None on:127
System / Step
H9 Bypass / off:None on:0
Mobius Bypass / off:None on:0
The button will cycle between both off, H9 on, Mobius on, and both on each time you press it. I might have the 127s and 0s reversed - don't remember if 127 means no signal or active signal on those devices.