You cant use your own coax. Its likely it wont be coax - rather their own cable from where the omnibox will be located on your outside wall around the house and up to the room where they will fit the surface box and the run Coax from that box to the 360. Other connections downstairs will come from there too. At least mine do.
As nodrogd says. fit a pull rope (strong string !) where you want the cable to run.
The Tech can then use that to pull their cable through and finish it off inside
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired, 1 WiFi, 1 on PA) Hub5 in modem mode with Apple Airport Extreme Router +2 Airport Express's. On 250Mbps, Talk Anytime Phone, x2 Mobile SIM only iPhones.