RCA Out To AES/EBU In To DAC

Get yourself a Monarchy Audio DIP (believe it stands for "Digital Interface Processor", there have been a few versions, they aren't very expensive new or used). This small, well-made box will take your S/PDIF and convert it to AES/EBU, while also providing electrical isolation between the source and DAC (just in case the spurious noise is caused by something else), as well as performing jitter-reduction. (Place the DIP away from other, line-level components to the extent that you can, particularly phono preamps.)

Yes, get the Monarchy DIP, not only does it solve your connection problem, but also reduces jitter... quite noticable improvement. You can find them used here on Audiogon ranging from $100-200 depending on type.

The Genesis Time Lens supports all the digital formats for input and the same on the output. Not only does it handle conversion from a transport to a DAC, its primary function to "realign" the datastream brings on a multitude of sonic improvements. At $400-500, this is an unbeatable solution.