The stabilizing action of nonlinear gain on dispersion-managed soliton transmissions is investigated. By means of a proper combination of nonlinear gain and filtering, the background and amplitude instability introduced by lumped guiding filters can be controlled. Indeed, radiative background that may not be separated from the signal when the average dispersion is close to zero is shown to be suppressed. Taking advantage of the large tolerance with respect to input energy variations, dispersion-managed solitons are found to be stable after collisions among different frequencies when supported by the same nonlinear gain element for all channels. This demonstrates the feasibility of nonlinear gain for wavelength-division-multiplexed transmissions and may open up the possibility of high-speed soliton transmission with large tolerance with respect to power fluctuations and densely packed wavelength channels.