Capacity requirements of the fixed access network keep increasing towards multi-gigabit connections. For Hybrid Fiber Coaxial (HFC) networks, aggregated rates around 30 Gbit/s can be achieved by increasing the DOCSIS spectrum to 3GHz, assuming a spectral efficiency around 10 bit/s/Hz. Replacement of spectrum limiting components such as passive taps in the HFC network is an efficient way to achieve these data rates, compared with the cost of fiber to the home (FTTH). Transmit amplifier distortion is a major issue in the extended-spectrum in addition to the high spread of attenuation between low and high frequencies. Existing spectrum allocation strategies are no longer applicable. This work presents a new method of spectrum optimization for the coax channel up to 3GHz, taking transmitter distortion into account in the optimization.