For parallel I think you need some sort of load sharing mechanism otherwise one converter will deliver most of the current, for series I’m pretty sure the output needs to be isolated.
Using those converters the simplest thing is IMO to create a dual output driver and have 2 separate LED channels, which is possible with multiple LEDs but also with XHP50/70 since they feature 2 separate strings of 2 series LEDs, the MCPCB needs to be modified though.
Another way is to use a boost regulator (external FETs) like LTC3786 with low RdsON FETs for higher power, several regulators can be put together to run several phases for a very high power single output boost converter. But with this even just one phase takes more space. Loneoceans GaN driver for example uses a boost regulator and well, GaN FETs, probably uses that regulator actually.