Asus rt-ac66u antenna replacement help

[elie776]

I have a Asus rt-ac66u everything is fine with it, but i have a somewhat of a large house and was thinking of replacing the antennas on it with bigger better ones 

 

i found some cheap ones on ebay http://www.ebay.com/itm/3-9dBi-RP-SMA-Dual-Band-WiFi-Antennas-Asus-Router-RT-AC66U-RT-N66U-RT-N16-AC1750-/141226998007

and this one http://www.ebay.com/itm/9dBi-RP-SMA-Antennas-3-for-Asus-RT-AC66U-Gigabit-AC1750-Router-USA-/141098026685

 

i was just wondering if they would work fine and increase my range as well their are 2 types of antennas (3.9dBi and 9dBi) which one is the best to get? 

 

i was reading through the page and saw that they only support IEEE 802.11a, 802.11b, 802.11g, 802.11n wireless LANs. not ac wireless is this a mistake or will they work with this??? 

 

thankyou 

[AMICLG]

To properly take full advantage of these you'll need to flash the router with DD-WRT and change the output power to a higher wattage but this it technically illegal under  FCC's rules.

[zapsyou]

Your better off getting a range extender

[FMQ203]

the first one are also 9dBi antennas, it says 3 9dBi antennas, 3 is the quantity