I should note, i use Balanced cables with my amps because i get an audible level of interference with RCA cables. I am not exactly sure where it is coming from, as this is the first house i have had this issue. However, with Balanced cables i get no interference, due to their construction and operation as John eluded to.
Also as John noted the lack of Balanced outputs on Oknyo products... I looked at the Onkyo website, the only product that i could find that has Balanced outputs was the PR-SC5508... Which receiver do you have?
