Can you confirm whether the DMX start address of the DMXcas is user adjustable, if I have two Casambi-controlled RGBW fixtures, each using 4 channels of DMX would I need 1 or 2 DMXcas connected to my DMX controller to drive them independently? The website says the unit can be configured as 8 individual channels, or would two units each have to be configured as RGBW?
The DMXcas is an RDM-compliant device, and it supports changing its start address (where it starts to use DMX slot data) via that RDM interface, or using the Casambi Vendor Parameter menu in the Casambi app. You are correct if you need more than 4 channels in the Casambi network to be controlled, you would need multiple DMXcas units to accomplish the transition from DMX to the Casambi network.
Casambi has threatened to come out with more than 4 channels of support this year, what was updated was the ability to toggle on/off more than 4 channels, i.e 8 channels with the toggle button on the app or other pushbutton in the Casambi network.
We have one customer that uses both the DMXcas and casDMX in his artistic lighting fixtures, he sometimes uses 150+ of EACH unit to get the mating down. One note is that he uses slow DMX transitions since fast ones overwhelm the Casambi network and basic commands are lost. In your case, you should be fine with a couple of DMXcas units.