Best results for me came when I stopped messing around with RCA connections, which are woefully ill-suited for transmitting digital audio data as they are almost never a true 75ohms, and replaced my RCA digital jacks with true 75ohm BNC on both ends and replaced the fancy audio RCA cable with a simple true 75ohm BNC industrial coax cable from Digikey, of the shortest length that would reach.
Crystal clear, smooth sound. About $12.00 for two BNC jacks and $22.00 for the cable. Can you believe in better sound for $34.00?
No secret here, you don't get objectionable reflections if the impedances are matched properly, so no magical lengths or materials are required.
PS: I DO believe in good quality audio cables for analog - I prefer Zu Event in my rig. Just relating my experiences with digital.