A method controls performance of modem arrangements wherein a plurality of tones having associated gains with a maximum reachable value are used for carrying respective bitstreams. The method includes at least one of selectively swapping bits between the tones in the plurality and selectively changing the tone gains to optimized an error parameter. The method also includes: determining the current values for the associated gain, determining the gain margins between the maximum reachable values and the current values, and performing, to optimize the error parameter as a function of the margins, at least one of: varying the number of bits allocated to the tones, and performing a transmitted power variation by varying the gains.