You cannot integrate with SEPM.
SEPM and Protection Engine for NAS are two completely different products and should be treated as such.
You can find the spec requirements along with other information here:
https://www.symantec.com/protection-engine-network-attached-storage
I would NOT recommend using one engine for 6 different locations, especially if they're all remote from one another. This would cause major performance issues.
The updates come down via LiveUpdate. They will not take updates from the SEP client.