Multiple Stream Limitations Question

If I have a Roon Core connected to multiple DACS (Each DACs output will connect to a source input on an eight-source/eight-zone whole-house audio system) what are the limitations of how many different songs can be played simultaneously? Is it the Core? The quality of a NAS drive?

Are you planning on upscaling music?
Upscaling can have a big effect on the network - e.g. streamiing to just one endpoint at DSD512 will be 50Mbps… sinple streaming of Redbook will be c1.5Mbps.
Upscaling/sampling will also place a load on the processor.
So, I think you need to provide more details about your Core (processor, RAM) and network.
Someone else might chime in and advise otherwise, but I don’t thing read speed of the NAS drive will be an issue.