I'm going to stick my head in here just to say AES/EBU Digital XLR typically carries same bits and bits as IEC 958 but being a professional connection is not subject to Digital Copy Management as is IEC 958 and optical S/PDIF. Most equipment I have, converting IEC 958 to optical S/PDIF is possible or S/PDIF to IEC 958; however, sometimes the receiving equipment may not be able to decode when sending a 24/96 signal from optical S/PDIF to an IEC 958 input which may only handle up to 16/48. Also, when going from RCA analog to XLR or XLR balanced to RCA you may have overload distortion seen as clipping. My advice, too many potential problems converting RCA to XLR analog, not so much converting IEC 958 to optical S/PDIF.