It depends. If the balance of your gear is fully differentially balanced then you will typically find some degradation in sound quality if you use the single ended inputs and outputs. Examples of this where it really makes a difference are brands like BAT, Ayre Acoustics, Esoteric, etc... If your system is not differentially balanced, the gear simply offers XLRs, then usually you will find the RCA connectors will sound as good or better unless there is a bad noise problem.
