In your place I buy a 2,5Gbit switch and 2x 2,Gbit USB adapters for your 2 NAS.
AX11000 2,5Gbit LAN > switch
NAS 1 with USB 2,5Gbit adapter > switch
NAS 2 with USB 2,5Gbit adapter > switch
Move device that is currently on the 2,5Gbit poort of the AX1000 to switch
Also take a look here...