Relaying Airport Extreme as a router with Peplink Balance 710

I did setup Airport Extreme as a just AP, not a router which can make a subnet further down that means I turned off NAT and DHCP from AE.
( Actually I have 6 AEs in our company.)

But I prefer actually using NAT, DHCP of AE as a router which can make a subnet further down in conjunction with Peplink Balance 710.

For by doing this way I could use NAT-firewall inside as well as making Mac OS X server management easier.
Mac OS X server can remotely manager AE’s NAT-PMP and DHCP for its integrity of management which I also prefer.

Not making double-NAT, is there a way to use NAT and DHCP to work with Peplink?

Only option I can think is using Peplink in drop-in mode but doing this way requires 3 WAN routers more as I have done a setup with 3 WAN ports from 3 ISPs now.

If anybody or staff knows a work around, please let me know !!!

Actually, you will not require 3 WAN routers. The router in the Drop-in mode document is representing as Internet gateway. The requirement is you need an additional static and public IP address on Peplink.