My Omnia is in a corner of the house (near my cable modem and server), and it has noticeably less full-bandwidth range on 2.4 GHz than the high-power AP/router it replaced. I don’t notice any difference on 5 GHz.
I figure I have two basic choices to increase antenna gain:
Change the antennas to higher gain omnis: http://www.ebay.com/itm/3-9dBi-RP-SMA-WiFi-Dual-Band-Antennas-for-Asus-RT-N66U-RT-AC66U-AC1750-D-link-/112048855825?_trksid=p2141725.m3641.l6368
Add some small Yagi elements to the existing antennas: http://ham-radio.com/k6sti/wifiyagi.htm
Or perhaps a combination of both.
At this point I’m leaning toward the Yagi simply to avoid dumping signal on my neighbors.