Your SMC router does have two mmcx antenna jacks inside the case. I own the Dlink 713p, which is a repackaged version of your router. You remove 4 phillips screws on the bottom, and carefully remove the top cover, and metal shield. You will see a pcmcia radio card with two antenna jacks at the end. These are mmcx connectors. I bought a 12 inch mmcx to n male patch cable, and connected it to a 8dbi omni. Works great. You could also substitute any other directional antenna you want. One note: of the two jacks on the radio card, the one closest to the center works best. The other connector off to the side of the card seems to be secondary, on my system it consistently performed worse than the center connector. Keep in mind this will void your waranty, and you also may need to drill a hole to pass the cable through the case, (I used one of the old useless antenna mount holes for this) so proceed with caution. If you are comfortable taking things apart and they usually work when you put them back together, this should not be too difficult for you. The link below is the company I bought the antenna (BS2400XL6) and patch cable (100M-NMMMX-12)from. Good luck.

http://www.antennasystems.com/broadband.html