The BCM4352 (AC/AN chip) is not supported, which is part of the reason to get one of these routers. Broadcom router chips are usually MIPS based, and also heavy on the binary blobs (which may allow for dd-wrt support).
Edit: In fact, I can't find any image that supports this BCM4352 on dd-wrt either:
http://wiki.openwrt.org/toh/asus/rt-ac56u
The BCM4352 (AC/AN chip) is not supported, which is part of the reason to get one of these routers. Broadcom router chips are usually MIPS based, and also heavy on the binary blobs (which may allow for dd-wrt support).
Edit: In fact, I can't find any image that supports this BCM4352 on dd-wrt either:
http://dd-wrt.com/wiki/index.php/Supported_Devices