I wonder, would z2m actually support multiple controllers? That could be interesting. Then again two containers is still simple.
I believe Z2M doesn’t; although not “out-of-the-box”.
See a discussion with the developer here.
But the easiest way seems to create a separate Z2M container with a slightly other name (i.e. “Zigbee2MQTT-basement”) that publishes to i.e. the “zigbee2mqtt-basement” topic (perhaps it’s even possible to use the same one if you keep the names different?)
In Homey you can then add a second “bridge” looking at the same MQTT server, evt at the zigbee2mqtt-basement topic.
When adding devices in Homey the are all alike for Homey and that way it seems one Zigbee network.
Would be a nice experiment. From what I’ve read on the internet, it should be possible this way.
Luckily the SLZB-06(/P7)’s are not that pricey. 
