are the barbettas powered speakers? if so then in that case they are only looking for a line input signal and in this case the instr.cable is fine. if as donM says they have the balanced or XLR connectors it IS definately worth the extra cost (or effort if making yourself) to run the balanced cables, but i would double check that they are not XLR connectors being used in place of 1/4' or speakons..many high quality passive speaker manufacturers use the XLR connector (but moreso the Speakon these days)because of its strength (physical) and the solid positive connection, but they are still only wired up as hot and cold (thru pins 1 and 3, with pin 2 not used) in normal balanced cables 2 is hot 3 is shield and 1 is cold.

peace, out