may be a "well know question", but I'm unable to find the right answer:
I built my own ap with 912UAG-2HPnD: three SIDs, three wlans with 2.4ghz and 5ghz NICs and everything seems work well: I can access all ssid flawless, surf on internet, limit the band for the guest access and applied few basic firewall rule to the wlans. In order to increase the range and also to add few wired connection, I bought a wAP AC, but I cannot figure out how connect the new ap. I searched on the net and also in this wiki, but no one right answer.
I'd like to know the right direction to achieve my goal.
 I forgot to say that the two ap can communicate only by wifi, not by wire.
Thanks in advance,
PS sorry for my poor english
Found the solution.. Not (may be) elegant, but functional: repeat for EVERY interface the WDS dynamic whit the same SSID.