Bundles of homogeneously alloyed Cu2-x(SySe1-y) nanowires with various compositions (0 <= y <= 1) are controllably prepared via a simple water-evaporation method under mild conditions. It is found that the nanowire bundles have similar copper contents (0.37 <= x <= 0.44) and morphologies, and the same face centered cubic (fcc) crystal structure and growth orientation of [110] over the entire composition range of y. To the best of the authors' knowledge, this is the first report on cubic phased ternary Cu2-x(SySe1-y) compounds. It is found that lattice parameter of the Cu2-x(SySe1-y) compound changes linearly with the S content. It is also shown that the direct and the indirect bandgaps of the nanowires vary quadratically with the S content and have bowing parameters of 0.20 and 0.21 eV respectively. Energy-gap-tuning via compositional change is achieved for both the direct (1.48-1.87 eV) and the indirect (0.50-0.90 eV) bandgaps. The trends of lattice parameter and bandgap variations are consistent with those described by Vegard's Law.