See 'WikiDevi' @ the Internet Archive (MW XML, Files, Images)
upgraded MW to 1.30 - maybe things are slightly less broken
AC1900 WiFi Range Extender
Web GUI: http://www.mywifiext.net
WI2 is not identifiable in the FCC photos but is assumed to be a Qualcomm Atheros QCA9984 or a QCA9980.
This device is based on the same QCA9558 platform as the Netgear EX7300 which is advertised as AC2200 (450+1733). The internal photos at the FCC for this device appear to be the exact same photos that were used for the EX7300 including the four front end chips for the an+ac radio.
There is some confusion about the actual supported speeds but it seems like Netgear is differentiating this EX6400 from the EX7300 by claiming slower 802.11n speeds of only 20 MHz channel width for the 2.4 GHz radio. It's not clear if 40 MHz channels are actually disabled in software.
The Netgear Press Release says, "AC1900 equals 216Mbps at 2.4GHz 802.11n + 1733 Mbps at 5GHz 802.11ac." The 216 Mbps speed likely comes from a 3-stream 20 MHz channel.
The User Manual claims, "Up to 300 Mbps for 2.4 GHz network and 1733 Mbps for 5 GHz network"
FCC document Test Report (NII).pdf claims: 802.11n speeds of up to 600 Mbps and 802.11ac speeds up to 1733 Mbps which is different from the AC1900 advertised class which some sources say corresponds to 600+1300 speeds. It would surprise me if the QCA9558 which supposedly provides bgn support actually supports the 600Mbps speed since it's only 3-stream and is too old to support 256QAM.
EX6400 / EX7300 Firmware Version 188.8.131.52 "Supports CE DFS Band 2 and Band 3."