If he has no noise with a lower voltage unbalanced system (i.e. RCA's), he will gain nothing by going with Symbilink or a line driver/higher voltage. The higher voltage potentially lowers the noise floor and increases SNR.....but if it's already at inaudible levels, then the net result is a lot of $$ spent for zero audible benefit.
Again; It's all about noise. If you have none using RCA's, then call it a day as you will not improve upon it in any way with Symbilink or a line driver.