Windows Access to my NAS with a Orbi - Cable Model setup

> >> IP Address 192.168.0.14, Connection DHCP, IP Subnet Mask
> 255.255.255.0, [...]

> >> 192.168.1.1, subnet 255.255.255.0, use router DHCP, starting .2
> ending .254.

   Ok.  Your main (outer) router is using "192.168.0.*" for its LAN, and
the Orbi (inner router) is using "192.168.1.*" for its LAN.

> >> found the option to assign a fixed IP.

   Did you stick with the ".14" address, or choose something more
memorable?  It's your choice.  I'll assume ".14" here, but you could
pick another.

   Now all you need to do is find where/how to specify a static route on
your main router.  The static route spec (on the main router) for this
situation should look something like this:

      Destination IP Address: 192.168.1.0
      IP Subnet Mask: 255.255.255.0
      Gateway IP Address: 192.168.0.14

   You may also need to specify a "Metric".  I'd pick "1", but on a
Netgear router, "2" might be as small as it lets you use.  (Or your
Selligent, I know nothing.)  With one extra route, it may matter little.

   An equivalent notation for "destination: 192.168.1.0, subnet mask:
255.255.255.0" would be "192.168.1.0/24".

   What that tells the main router is that a message with a destination
address of "192.168.1.x" (0 <= x <= 255) should be sent to
"192.168.0.14" (the Orbi WAN/Internet interface), instead of to its
usual default destination (your ISP).

   The Orbi (inner router) doesn't need any special instruction,
because, by default, it sends anything foreign-looking out its
WAN/Internet interface, which goes to your main router.  Your main
router already knows what to do with any destination on its own LAN
("192.168.0.*"), and anything else should be sent to your ISP.

   What could go wrong?