I had a similar set-up as you describe. You will still need the modem function of your modem router to supply the internet signal from TimeWarner, but if you connect via ethernet from your existing modem router to the ORBI system, you should get a stronger system and better speed. I'm not with TimeWarner, but I had purchased and was using a modem router. After installing ORBI as described above, the strength and speed of my signal increased measurably. Remember that the wifi cannot make the speed greater than what arrives via your provider, but a better system, such as the ORBI, can bring the wireless signal closer to the actual ethernet speed. That's what it did for me.