It's a minor technicality. Generally, any product with an RCA/phono type digital connector (usually called "S/PDIF" or "coaxial") is compatible with MasterLink. Few professional products actually use a true S/PDIF protocol, which was developed by Sony and Philips (hence "S/P Digital Interface Format"). S/PDIF's maximum word length is 20 bits, it includes the Serial Copy Management System (SCMS) copy protection bits, and it can carry index markers and start IDs in its subcode. IEC958 is basically the same data stream as AES/EBU, but electronically is unbalanced, at a lower voltage, and on a coaxial connector.