Methods and systems for optimizing the transmission of superchannels with different modulation formats may include pre-calculating different guardband (GB) values between superchannels and sets of power values for subcarriers to implement subcarrier power pre-emphasis (SPP). When a request for an optical path is received at a network management system, the spectral allocation of each superchannel, including a GB, is determined according to pre-specified rules based on co-propagation of the superchannels with different modulation formats.