Hi,
Another thing to consider is how many rooms in the house have cable jacks. Most likely that outside cable is connected to a splitter, or possibly several splitters, and then feeding lines to multiple rooms pre-wired in that new house. Those splitters and all those extra lines could cause strange things to happen trying to use it for an outside antenna.
If the home has a basement, you can probably see the wiring and splitters. If not, everything is probably hidden behind the walls or possibly in an attic, often hidden under insulation. Since you had the house built, you probably have access to the construction plans and details that might help.
If you can isolate just the outside line and use just that with a direct line to an inside connection, it might possibly work for you as described with the good advice in the post above.
Regards,
-Dan